The increase in urinary albumin excretion rate (AER), a hallmark of both diabetic nephropathy and hypertension, has also been described in patients affected with diffuse psoriasis. The aim of this study was to investigate whether such an increase is independent of the coexistence of diabetes or hypertension and whether it may be related to the extension and severity of skin lesions. Median AER, determined by radioimmunoassay, was significantly higher in a group of 32 normotensive nondiabetic psoriatic patients than in 36 age- and sex-matched controls (9.6 vs. 5.3 micrograms/min; p = 0.0006). AER was related with grading of skin involvement (r = 0.65; p = 0.001); patients with the most widespread skin lesions (psoriasis area and severity index: PASI greater than 11) were characterized by a significantly raised median AER (14.9 micrograms/min) compared with those with PASI scores between 4 and 11 (9.8 micrograms/min) or less (5.6 micrograms/min) and controls (F = 10.58; p = 0.0001), independent of other covariates such as age, sex and blood pressure (p = 0.001). This latter finding was confirmed by the prevalence of microalbuminuria (AER greater than 10 micrograms/min) which was present in 2 out of 8 patients with PASI less than 4, 0 out of 12 patients with PASI ranging between 4 and 11 and in 5 out of 12 psoriatics with PASI greater than 11 (p = 0.038 by two-tailed Fisher's exact test).