Background: Lupus erythematosus (LE) and porphyria cutanea tarda (PCT) may have similar clinical presentations, and their coexistence presents special problems in diagnosis and management. Objective: The purposes of this study were to describe a patient with discoid LE and PCT and to present a review of 15 patients with coexistent LE (all variants) and PCT. Methods: The medical records of all patients with coexistent LE and PCT seen between 1976 and 1995 were retrospectively reviewed. Results: Of 6179 cases of LE and 676 cases of porphyria (all variants), there were 15 patients, 6 men and 9 women, with coexistent LE and PCT. The mean age at diagnosis of LE was 42.8 years and of PCT was 48 years. Nine patients had discoid LE; five patients had systemic LE, and one patient had subacute cutaneous LE. The initial diagnosis was LE in eight patients, PCT in five patients, and simultaneous LE and PCT in two patients. Precipitating factors for PCT included alcohol in seven patients, iron overload in one patient, and estrogen in one patient. Treatment of LE with hydroxychloroquine 200 mg daily precipitated PCT in two patients. Patients were treated with phlebotomy or low-dose antimalarials for PCT. Patients with systemic LE received systemic glucocorticoid therapy. Patients with discoid LE and subacute cutaneous LE were treated with topical glucocorticoids. Conclusion: The association of LE and PCT poses therapeutic challenges. The preferred treatment for one may exacerbate the other. Use of standard dose antimalarials for LE is inadvisable, and phlebotomy or low-dose antimalarials should be used cautiously in patients with coexistent disease. (J Am Acad Dermatol 1998;38:569-73.)