BACKGROUND: Genetic factors play an important role in susceptibility for psoriasis. The angiotensin I-converting enzyme (ACE) is expressed by keratinocytes. Administration of ACE inhibitors may induce or exacerbate psoriasis in clinical practice. Thus, ACE gene variants may contribute to the genetic background of psoriasis. OBJECTIVES: To assess the role of the ACE insertion/deletion (I/D) polymorphism in psoriasis among ethnically Chinese Taiwanese subjects. METHODS: In total, 312 patients with psoriasis and 615 control subjects were analysed for the ACE I/D polymorphism by polymerase chain reaction. RESULTS: A marginally significant difference (P=0 x 035) was found in the distribution of ACE I/D genotype frequencies between patients with psoriasis and controls. The frequency of the II genotype in patients with psoriasis was significantly higher than that in the control group (55 x 1% vs. 46 x 7%, respectively, P=0 x 015). Although the I allele frequency in patients with psoriasis (72 x 4%) was higher than that in the control group (68 x 2%), the difference was not significantly different (P=0 x 062). After adjusting for age and gender, carriers of the II genotype were 1 x 45 (95% confidence interval 1 x 09-1 x 92) times more likely than noncarriers to have psoriasis (P=0 x 010). CONCLUSIONS: Our results suggest that the presence of the I allele may confer susceptibility to development of psoriasis among ethnically Chinese Taiwanese individuals.