OBJECTIVE: To explore the clinical characteristics of hyperglycemia in patients treated with quetiapine. METHOD: A pharmacovigilance survey of spontaneously reported adverse events in quetiapine-treated patients was conducted using reports from the U.S. Food and Drug Administration MedWatch program (January 1, 1997, through July 31, 2002) and published cases using the search terms hyperglycemia, diabetes, acidosis, ketosis, and ketoacidosis. RESULTS: We identified 46 reports of quetiapine-associated hyperglycemia or diabetes and 9 additional reports of acidosis that occurred in the absence of hyperglycemia and were excluded from the immediate analyses. Of the reports of quetiapine-associated hyperglycemia, 34 patients had newly diagnosed hyperglycemia, 8 had exacerbation of preexisting diabetes mellitus, and 4 could not be classified. The mean +/- SD age was 35.3 +/- 16.2 years (range, 5-76 years). New-onset patients (aged 31.2 +/- 14.8 years) tended to be younger than those with preexisting diabetes (43.5 +/- 16.4 years, p = .08). The overall male:female ratio was 1.9. Most cases appeared within 6 months of quetiapine initiation. The severity of cases ranged from mild glucose intolerance to diabetic ketoacidosis or hyperosmolar coma. There were 21 cases of ketoacidosis or ketosis. There were 11 deaths. CONCLUSION: Atypical antipsychotic use may unmask or precipitate hyperglycemia. UPDATE: An additional 23 cases were identified since August 1, 2002, the end of the first survey, by extending the search through November 30, 2003, bringing the total to 69.