Information from the Ohio Department of Mental Health (ODMH) database was reviewed retrospectively to identify patients at the Cincinnati center treated with an atypical antipsychotic and who had also been evaluated or treated for diabetes mellitus. Blood glucose levels, glucose tolerance, or other evaluations of diabetes had been conducted in 14 of the 126 patients treated with atypical antipsychotics. In 11 of the 14, new-onset, acute, and marked glucose intolerance developed after treatment with clozapine, olanzapine or quetiapine. Of these, six patients required insulin therapy (four only transiently) and five patients developed diabetic ketoacidosis (DKA). Also, glucose metabolism was labile in all cases, and was transient in two cases with subsequent resolution despite on-going antipsychotic therapy. Certain atypical antipsychotics may be associated with new-onset glucose intolerance, including acute diabetes and ketoacidosis. Monitoring for changes in blood glucose levels in patients taking atypical antipsychotics may be indicated. More systematic study data are clearly needed.