Antimalarial drugs, like chloroquine, may produce hyperpigmentation of the oral mucosa, affecting most commonly the palate. Its pathogenesis is not clear; an increased production of melanin is currently believed to be the cause of this oral manifestation. The purpose of this study was to report a case of atypical oral mucosal hyperpigmentation secondary to antimalarial therapy. A 66-year-old, dark skinned woman was evaluated for oral pigmentation. The patient had a history of chloroquine therapy, and presented a diffuse blue-gray pigmentation in the hard palate and, mainly, in the lower lip. Diagnostic hypothesis were of physiologic pigmentation, drug-induced pigmentation, pigmentation associated with systemic diseases, smoker's melanosis and post-inflammatory pigmentation. Incisional biopsy was conducted and histopathological examination revealed lichenoid dermatitis and pigment incontinence. Fontana-Masson staining was positive for melanin, but Perl's iron staining was negative. The histopathological diagnosis was consistent with melanin incontinence related to drug-induced lichenoid reaction secondary to chloroquine therapy. Adequate correlation of clinical and microscopic aspects was essential for the definitive diagnosis, especially in atypical cases. This diagnosis is of great relevance for the patient, since the oral manifestation might be an early sign of ocular complications due to antimalarial therapy. Therefore, the identification of these oral manifestations indicates regular evaluations by an ophtalmologist, preventing greater complications of antimalarial therapy for the patient.