Cutaneous protothecosis developed in a 63-year-old Japanese female. The patient had a long history of steroid use for bronchial asthma. A tender, swollen, erythematous plaque with white papules covered the dorsal aspect of the patients right hand. Histopathological examination showed typical protothecosis with numerous mulberry-like sporangia positive for periodic acid-Schiff stain. The pathogen was identified as Prototheca wickerhamii. After a 6-week course of 150-200 mg/day itraconazole (ITCZ) therapy, the patients culture was negative for P. wickerhamii. No recurrence was seen after 12 weeks of ITCZ therapy. This case of protothecosis and those of 16 patients are summarized. All the patients had lived in mid- to southern Japan. Only 12 cases of protothecosis treated with ITCZ have been reported in the literature; 8 of these cases were cured with ITCZ therapy alone. In cases treated with ITCZ at no more than 100 mg/day, medication was typically needed for 2 months; most of the cases treated with ITCZ at 200 mg/day were successfully cured within 2 months. A 2-month course of ITCZ at 200 mg/day appears to be adequate treatment for human protothecosis.