The clinical diagnosis of Hallopeau's acrodermatitis (HA) restricted to nail and digital pulp may be difficult, and even dermatologists often fail to recognize this condition. The aim of this study was to review the clinical and pathological features of 20 patients, observed over a period of 5 years (1988-1993), who were affected by HA limited to the nails. Our study shows that HA of the nail unit more commonly affects middle-aged females. In all our patients HA of the nail was restricted to one digit and not associated with other manifestations of pustular psoriasis. HA of the nail unit is characterized by a chronic course. None of our patients had a complete clearing of the dermatitis during the follow-up period. In 4 patients the acute phases of HA were treated with the non-steroidal anti-inflammatory agent nimesulide 200 mg/day, with great improvement of inflammatory signs and subjective pain within a few days. In these patients, prolongation of treatment with nimesulide during remission phases prevented relapses of the dermatitis.