BACKGROUND: Phototherapy, PUVA therapy and narrow-band UVB are recognised forms of first-line therapy for extensive and severe plaque psoriasis. Based on a systematic review of the medical literature, we propose a good practice guideline for the use of narrow-band UVB phototherapy in this indication. METHODS: We carried out a review of the literature published over the 20 years (1998 to 2009) in the online PubMed database. Our conclusions are based on the results of control studies or where these are absent, on a synthesis of the recommendations common practice approved by the experts of the French Society of Photodermatology. The levels of scientific proof given are based on the criteria defined by Sackett. RESULTS RECOMMENDATIONS: (1) Practical aspects. Irradiation cabins equipped with Philips TL01 tubes, either for monotherapy (42 tubes) or for combined therapy (21 UVB tubes and 21 UVA tubes), were to be certified (CE marking, ISO-DIN certification) and equipped with an accurate dosimetry system. Several valid and usable protocols exist. The indication was based on the severity and extent of the episode of psoriasis, the psychological consequences of the dermatosis, comparison of the benefit/risk ratios of the various available treatments, the ability of the patient to attend sessions (a vital factor in therapeutic compliance), the cumulative doses of UV from previous courses of treatment, and absence of contraindications, including the use of photosensitising medication. Informed consent was to be obtained from patients, who were given a validated information sheet (available at www.sfdermato.org). The study results and the value of maintenance therapy were not confirmed. (2) Adverse effects. The immediate adverse effects were generally of little consequence, with later effects alone posing problems. Because of the risk of induction of cataract, ocular protection must be used during sessions. In the absence of symptoms or known ocular disorder, prior ophthalmologic control is not considered necessary. The risk of skin cancer remains poorly defined, and this risk has not been clearly shown to be lower than with broad-spectrum UVB therapy or PUVA. The studies give no indication of the number of sessions after which therapy must be completely discontinued. In the absence of clear evaluation of oncogenic risk, it seems reasonable to set the maximum number of sessions of UVB TL01 phototherapy at 250 as with PUVA, and to include in this limit the total of all PUVA and TL01 phototherapy sessions for patients receiving both types of phototherapy (level of proof: B). In the absence of lesions requiring treatment in these areas, the face and male genital organs should be protected during treatment sessions. There is no currently available data concerning carcinogenic risk induced by TL01 in patients also on cyclosporine, methotrexate or biotherapies. In order to reduce risk and maintain patients' capacity to undergo further phototherapy sessions, we suggest (level of proof: A) the following measures: strict patient selection, use of combined synergistic therapies, annual examination of the skin and appendages of subjects receiving more than 150 phototherapy sessions, and the creation of nationally accessible patient phototherapy files. (3) Combined treatments. The purpose of such treatment is twofold: to reduce the risk of adverse effects while increasing the efficacy of TL01 phototherapy. Lesions should be sloughed before the start of phototherapy. Synergistic effects have been demonstrated for dermal corticosteroids and tazarotene, but such effects are less noticeable with topical vitamin D3 derivatives. If there are no contraindications to its prescription, we feel that acitretine has demonstrated efficacy in enhancing the effect of TL01 phototherapy. (4) Efficacy. Narrow-spectrum UVB phototherapy is considered highly effective in extensive psoriasis. At a rate of three sessions per week, it results in complete (or almost complete) eradication of lesions in 60 to 90 % of patients within 20 to 40 sessions (level of proof: A). However, the efficacy of this therapy varies according to plaque size and noticeably better results are obtained in guttate and nummular psoriasis than in psoriasis involving large plaques. CONCLUSION: Narrow-spectrum UVB phototherapy offers a good alternative to PUVA therapy since concomitant psoralen is not required, but there are few immediate adverse effects, there is less risk of drug-induced photosensitisation, and there is no need for skin or ocular photoprotection after sessions. We recommend this approach as the first-line phototherapy (level of proof: A) in children and adolescents, and in adults with extensive moderate psoriasis involving small superficial plaques. It may also be used in pregnant or breastfeeding women and in patients with renal or hepatic insufficiency. In addition, it is preferable for HIV-positive subjects (level of proof: C). However, PUVA therapy is preferable as first-line treatment in extensive severe psoriasis involving large thick plaques (level of proof: A) and in adults of phototypes IV to VI (level of proof: B); it should also be contemplated for psoriasis refractory to UVB TL01 (level of proof: B).