After observing a patient with adult-onset tooth discoloration coincident with minocycline administration, we retrospectively surveyed a cohort of patients with severe cystic acne during therapeutic trials with isotretinoin. Four of 72 patients who had minocycline therapy during adolescence were found to have minocycline-associated tooth discoloration, which occurred in one case after only four weeks of treatment. Thus, minocycline must be considered as an uncommon cause of tooth staining in adults.