BACKGROUND: Smoking is a well known risk factor for cardiovascular, lung and many other diseases. Smoking can induce pulmonary arterial hypertension (PAH) in animal models and PAH is common in smokers with chronic obstructive pulmonary disease (COPD) and thereby not correlated to the degree of airway obstruction. The impact of tobacco smoke exposure on the development of PAH in human is not known. METHODS: In a case control study we assessed smoking and secondhand smoke exposure in all patients with PAH and chronic thromboembolic pulmonary hypertension (CTEPH) seen at our PH clinic from 2002 until July 2008. Data from PAH-patients were compared with CTEPH and healthy controls from the Swiss health survey 2007 (SHS). RESULTS: 91 PAH-patients were compared with 64 CTEPH-patients and 18747 controls (women 58, 36, 10331 respectively). Tobacco smoking was significantly more common in PAH compared to CTEPH and controls. This difference could be attributed to men. PAH-patients also smoked longer and heavier compared to CTEPH. In addition, secondhand smoke exposure was significantly longer in PAH-non-smokers compared to controls. CONCLUSION: Our data indicate that tobacco smoke exposure may be a risk factor for men with PAH. Considering smoking as a risk factor for PAH will have implication in counseling patients and especially their hitherto unaffected relatives. Further research on the pathogenetic role of smoking in PAH is warranted.