BACKGROUND: Psoriasis is a highly heritable disease. It has been suggested that psoriasis is preferentially transmitted from fathers.AIM: To evaluate the degree of familial aggregation of psoriasis; to determine the recurrence risk ratio (λR ) of psoriasis in first, second and third degree relatives of patients with psoriasis; and to investigate the transmission patterns of the disease and their relationships with the clinical profiles of patients.METHODS: A cross-sectional study on 640 consecutive, unrelated adult patients with chronic plaque psoriasis was performed. The prevalence of psoriasis in first, second and third degree relatives of the patients was determined, and the λR was calculated under the assumption of a population prevalence of 2%. Age of onset and presence of facial, hand and foot psoriasis were evaluated in probands with paternal vs. maternal transmission.RESULTS: A positive familial history of psoriasis was found in 380 patients (59.37%). Of these, 174 (27.18%) had at least one parent with psoriasis, with a λR of 13.59, while 106 patients (16.56%) had at least one second degree relative with psoriasis, and 34 patients (5.31%) had one third degree relative with psoriasis. No parent-of-origin effect in transmission of psoriasis from affected parent to offspring was observed, and there were no significant differences in the clinical profiles of the disease between patients grouped by transmission pattern of psoriasis.CONCLUSIONS: These results show a high familial recurrence risk of psoriasis, and suggest a balanced parental transmission of the disease.