Psoriatic arthritis is a frequent manifestation of psoriasis, and has a high level of impact on physical functioning, work ability and quality of life. However, there have been few studies of the epidemiology, development of and risk factors for concomitant psoriatic arthritis in patients with psoriasis. This study analysed data from a German public health insurance database of > 2 million individuals. Factors influencing the development of psoriatic arthritis were determined by descriptively analysing comorbidities and Cox regression modelling. The prevalences of psoriasis and psoriatic arthritis were 2.63% and 0.29% in adults (18+ years) and, respectively, 0.30% and 0.01% in children (0–17 years). The proportion of adult patients with incident psoriasis who developed concomitant psoriatic arthritis within five years after diagnosis of psoriasis (mean 2.3 years) was 2.6%. Cardiovascular diseases are the most frequent comorbidity in patients with psoriasis with or without concomitant psoriatic arthritis. Depression and neurosis/stress disorder were identified as indicators for the development of psoriatic arthritis.