Minoxidil overdose occurs infrequently and little toxicity data are available. This study examines the epidemiology and clinical toxicity of minoxidil exposures to both tablets and topical solutions. All cases reported to the American Association of Poison Control Centers (AAPCC) Data Collection System from 1985 to 1991 were reviewed with respect to patient age, reason for and route of exposure, dosage form, co-ingestion, healthcare facility (HCF) referral/admission, treatment and medical outcome. 285 cases were reviewed. 145 (51%) occurred in children less than 6 years of age. 273 (96%) exposures were acute, 239 (84%) were accidental, 224 (79%) occurred via ingestion and 61 (21%) involved co-ingestion. 130 (46%) patients were referred to an HCF and 32 (11%) were admitted. The outcomes were: minor/no effect 59%, moderate 4.2%, major 1.8%, and 1 death. All topical exposures resulted in minor to no effects. Of 224 ingestions, 16 (7.1%) developed significant toxicity defined as moderate/major effects [AAPCC criteria] or death (one case involving tablets). In these 16 cases, 69% were intentional and 13 (81%) involved co-ingestion; the most frequent effects were hypotension (69%), tachycardia (38%) and lethargy (31%); 44% received intravenous fluids and vasopressors. Only 2 cases of hypotension were attributable to minoxidil alone (no history of co-ingested drugs); both responded to intravenous fluids and dopamine. The only death was a suicide, with co-ingestion of hydralazine, prazosin and paracetamol; terminal symptoms were intractable hypotension, coma and pulmonary oedema. It is concluded that significant toxicity after minoxidil exposure, regardless of formulation, is associated with oral administration, intentional exposure and co-ingestion of other agents.