The aim of this study was to determine factors associated with regular use of inhaled corticosteroids (ICS) by asthmatic patients in primary care practices. A cross-sectional survey was carried out over 12 family practices in the Philadelphia greater Metropolitan area. A total of 394 patients aged 18-49 years, who received medical care for asthma from their primary care physician and had been prescribed ICS between 1 January 1995 and 31 December 1996, were included. The study measured self-reported demographics, experience with asthma, use of and attitudes about ICS, and health beliefs in six domains. Only 38% of patients reported using ICS at least twice a day almost every day. The most frequently cited reasons for inconsistent or non-use of ICS were related to a belief that ICS were unnecessary during asymptomatic periods and to a general concern about side-effects. By logistic regression, factors associated with regular use of ICS were two patient health beliefs, namely the health belief of 'Active' participation in clinical decision-making with their physician (OR = 4.6, 95% CI 2.8, 7.5), and the health belief that asthma was a 'Serious' health problem (OR = 2.3, 95% CI 1.4, 3.7), and hospitalization for asthma within the previous 12 months (OR = 2.3, 95% CI 1.6, 4.6). Patients were more likely to report regular use of ICS if they saw themselves as active participants in their treatment planning and conceptualized asthma as a potentially serious illness. These results support the themes of patient education and shared decision-making between patients and physicians that are promoted by the Asthma Guïdelines from the National Heart, Lung and Blood Institute (NHLBI).