Hereditary susceptibility and allergen exposure have been identified as general risk factors for asthma. However, risk factors for severe asthma still remain to be identified. To further assess and quantify risk factors associated with severe asthma in adult patients apart from clinical exacerbations, 306 randomly selected subjects (mean age 40+/-17 years, 46% males) presenting to an inner city pulmonary practice between 1995 and 1996 were retrospectively investigated. Of these, 117 patients were atopic, 112 had current asthma, and 22 asthmatics had severe asthma. Risk factors associated with atopy were family history of atopy and any domestic pet ownership (OR: 3.1, 95% CI: 1.64-6.1). Asthma was generally associated with atopy (OR: 4.2, CI: 2.4-7.4) and pet ownership (OR: 2.4, CI: 1.2-4.6). Severe asthma was strongly associated with current smoking (OR: 4.8, CI: 1.3-18.3), and lung function was negatively correlated with the amount of consumed cigarettes per day (r = -0.61, p = 0.04). However, no association with sensitization to Alternaria was found in severe asthma. Cigarette smoking is an independent risk factor associated with severe asthma in urban patients, whereas sensitization to Alternaria is of less importance in these patients.