We have examined smoking habits in 108 patients with psoriasis, including some with palmoplantar distribution, and compared the results with matched controls from the community. There was a significant association between psoriasis, current smoking status (OR = 2.7, 95% CI 1.44-5.42, P less than 0.01) and smoking habits prior to the onset of disease (OR = 3.75, 95% CI 1.68-9.47, P less than 0.001). There was also a marked dose-response relationship; the relative risk of psoriasis in those currently smoking more than 20 cigarettes/day was significantly elevated (OR = 5.3, 95% CI 2.1-13.0, P less than 0.001). Separate analysis of patients without palmoplantar distribution of psoriasis showed a significant association with smoking prior to onset of psoriasis (OR = 3.6, 95% CI 1.5-9.8, P less than 0.001). Smoking may play a role in the aetiology of this common skin disorder.