The aim of this study was to assess the degree of asthma control according to GINA criteria during two different seasons in Spain. An multicenter, longitudinal, epidemiological study with the participation of a sample of physicians in Spain was conducted. Consecutive asthma patients, 18 years of age and older, seeking primary and specialist care were included in the study. Patients were seen during the winter and spring 2004 and were asked about asthma control according to GINA control criteria (daytime and nighttime symptoms, asthma exacerbations, limitations of physical activity, and visits to the emergency department) during the 4 weeks prior to the visit. Control was defined according to daytime and nighttime symptoms. A total of 614 patients participated in the study. The proportion of patients reporting daytime symptoms "every day" or "most days" during the winter versus spring was 40.1% vs. 23% (P<0.01); 26.9% vs. 14.1% presented symptoms at night (P<0.01); 11.5% vs. 8.3% had severe exacerbations; 33.5% vs. 35.7% presented symptoms accompanying exercise, and 9.4% vs. 4.3% (P<0.01) had required emergency visits. The number of patients with inadequate control was slightly higher in winter than in spring (74.4% vs. 71%) (P<0.01). The most commonly prescribed treatment was ICS plus LABAs for both periods. Asthma is poorly controlled in Spain and strategies are needed to improve management of this illness.