Mesotherapy with hyaluronic acid (HA) is a treatment approach currently used for skin rejuvenation. High-frequency ultrasound (20-100 MHz) is a non-invasive technique that has been used to evaluate age-related dermal changes. The presence and the degree of a typical subepidermal low-echogenic band (SLEB) are photoaging related: the lower the SLEB echogenicity, the higher the photoaging. The aim of this trial was to evaluate, through ultrasound imaging, the long-term effects of microinjections of HA on SLEB echogenicity. Twenty-two women with clinical and ultrasound signs of moderate photoaging were enrolled in the study. Treatment consisted of multiple microinjections of HA salts of biotechnological origin on the dorsum of one hand, once weekly for 4 weeks and, successively, once monthly for 4 months (group A) or 9 months (group B). The dorsum of the other hand of each subject was injected with saline solution and used as a control. In all subjects, high-frequency ultrasound (22 MHz) was performed to evaluate SLEB echogenicity changes during treatment. Eighteen out of 22 patients completed the study. At the end of 4 weeks, an ultrasound increase of dermal echogenicity was observed in 13 subjects (seven of group A and six of group B), which we considered as "responders". In these patients, the Student's t-test showed a significant increase from baseline of SLEB pixel numbers of +24 % (P < 0.01) versus +6 % with placebo. In the same subjects, after an additional 4 months of monthly injections, the mean increase was +18 % (P < 0.05) versus +4 % with placebo. In patients from group B that completed 10 months of treatment, the increase from baseline of SLEB pixel numbers was +18 % (P < 0.05) versus 0 % with placebo. Our study suggests that mesotherapy with HA may effectively improve skin aging and photoaging, as supported by quantifiable ultrasound data showing significant changes in SLEB density over time.