SUMMARY Purpose: After observation that asthma is more frequent in psoriatic patients than in general people the aim of this study was the determination of any correlation between asthma and psoriasis and the investigation of the association between psoriasis severity and extent of respiratory function disorder. Material and methods: The study included 57 patients with psoriasis. After their separation in two groups, according to clinical history of asthma or not, spirometry was performed in all patients and FEV1, FVC, FEV1/FVC and MMEF were recorded. Then patients underwent dermatologic consultation in order to confirm the severity of psoriasis by three parametres namely, erythema > 1, injuries infiltration, clinical stability or activation of illness. Results: Twelve out of 57 patients have had clinical history of asthma. The mean FEV1 value (as a percentage of predicted) was 81.08% in asthmatic patients and 98% in the other group. Normal ratio FEV1/FVC was found in 60% (18/30) of the patients with erythema > 1 and in 88% (22/25) with erythema  1. Normal FEV1/FVC ratio was also found in 68,75% (33/48) of the patients with infiltration in psoriatic injuries and in 100% (7/7) of those who had not. In addition, normal FEV1/FVC ratio was observed in 59,9% (13/28) of the patients with active psoriasis and in 81,8% (27/33) of those with stable disease. MMEF (maximum midexpiratory flow rate) was normal in 36,3% (8/22) of the patients with active psoriasis and in 60,6% (20/33) of those who were clinically stabilized. Conclusions: Our data reveal an evident correlation between psoriasis severity and extent of respiratory function disorder. Psoriasis and asthma might correlate through a common pathogenetic pathway that needs to be studied. Pneumon 1999, 12 (1): 46-51