Bazex syndrome (acrokeratosis paraneoplastica) is characterized by a psoriasiform eruption that favors acral sites and has been associated with an underlying malignancy in all reported cases. Of the 93 patients in this series, 89 were male with a mean age of 60 +/- 8.5 years. Squamous cell carcinomas of the head and neck and squamous cell tumors of unknown primary with cervical lymph node metastases were the most commonly associated neoplasms, suggesting that the factor(s) responsible for the development of the syndrome are relatively specific for tumors of the upper aerodigestive tract. The cutaneous lesions were erythematous to violaceous in color and had associated scale; the most frequently observed sites of involvement were the ears, nose, hands, and feet, including the nails. In 63% of the cases, the cutaneous lesions preceded the initial symptoms or diagnosis of the tumor by an average of 11 months (range, 1-72) and, in general, the eruption was resistant to a variety of topical treatments. Occasionally, a reappearance of the papulosquamous lesions signaled the recurrence of the tumor (6 cases) or the appearance of skin lesions coincided with the development of metastatic disease (3 cases). In 91% (64/70) of the patients, the skin eruption either improved significantly following treatment of the underlying malignancy or did not improve in the setting of persistent tumor. However, even when all of the skin lesions cleared, the nail dystrophy often persisted. Fifteen of the patients developed vesicles, bullae, and crusts in addition to papulosquamous lesions. Possible explanations include the formation of an epidermal-dermal split via a bullous lichen planus-like mechanism, or the coexistence of two diseases; i.e., acrokeratosis paraneoplastica plus either porphyria cutanea tarda, bullous pemphigoid, or epidermolysis bullosa acquisita. One possible explanation for the development of the characteristic cutaneous eruption is an immune reaction, humoral or cellular, directed against a common antigen present on the tumor and the normal skin. Alternatively, tumor production of a keratinocyte growth factor such as TGF-alpha may be involved in the induction of the psoriasiform skin lesions.