The aetiology of lichen planus is unknown, but it is often connected with infections. In recent years peptic ulcer disease has also been closely linked with an infectious agent, Helicobacter pylori. A case-control study was conducted in 78 patients with lichen planus to find out a previous history of peptic ulcer disease, using a questionnaire and a medical record review. Patients were also asked about family history in first- and second-degree relatives. Fifty-seven patients with other skin diseases were interviewed as controls. The prevalence of H. pylori infection in patients with lichen planus was compared to that of 39 patients with other skin diseases and to the overall prevalence rates of H. pylori infection in Finland. Our findings are consistent with an approximately three-fold increased risk of peptic ulcer in patients with chronic/repeating lichen planus, when compared to the control patients (p = 0.04) and also to the overall peptic ulcer prevalence rates in Finland. Forty-one percent of the patients with chronic/repeating lichen planus had a first- or second-degree family member with a peptic ulcer, while the corresponding rate in the control group was only 12% (p=0.003). The prevalence of H. pylori infection in patients with chronic/repeating lichen planus and transient lichen planus was not significantly different from that in patients with other skin diseases.