The objective of this study was to investigate the prevalence of nasal polyposis in Greek patients with chronic rhinitis and asthma. We studied 3817 patients (2342 men and 1385 women) who were referred for allergy evaluation during 1990-1998 and diagnosed as having chronic rhinitis and asthma. Skin-prick tests with allergens common in Greece and controls were used in all subjects. A wheal with a mean diameter > or = 3 mm was considered as positive. According to the history of symptoms and the results of skin tests, patients were divided into the following groups: patients who have allergic rhinitis (seasonal, perennial), patients who have allergic asthma (seasonal, perennial), patients who have nonallergic rhinitis, and patients who have nonallergic asthma. All patients were examined for nasal polyps by anterior rhinoscopy and endoscopic investigation with a rigid or/and flexible endoscope. We found that 4.2% of the patients with chronic rhinitis and asthma (4.4% of the men and 3.8% of the women; p > 0.05) had nasal polyps. The prevalence of nasal polyps increased with age (p < 0.001) in both sexes. The prevalence of nasal polyps was 13% in patients with nonallergic asthma, 2.4% in patients with allergic asthma, 8.9% in patients with nonallergic rhinitis, and 1.7% in patients with allergic rhinitis. Nasal polyps were found in 3.6% of the patients with rhinitis and in 4.8% of the patients with asthma (p > 0.05). Nasal polyps were present more frequently (1) in patients with nonallergic respiratory disease (rhinitis, asthma) than in patients with allergic respiratory disease (10.8% versus 2.1%; p < 0.001) and (2) in patients with perennial respiratory allergy (rhinitis, asthma) than in patients with seasonal respiratory allergy (4.8% versus 0.4%; p < 0.001). We found that 4.2% of patients with chronic rhinitis and asthma had nasal polyps. Nasal polyps were present more frequently in nonallergic patients than in allergic patients and in patients with perennial allergy than in patients with seasonal allergy.