BACKGROUND Severe tardive dyskinesia (TD) represents a serious and potentially disabling movement disorder, yet relatively little is known about the incidence of and risk factors for severe TD.

METHOD We report the results of a longitudinal prospective incidence study of severe TD in 378 middle-aged and elderly neuropsychiatric patients. Psychiatric, neuropsychological, pharmacological and motor variables were obtained at intake and at regular intervals for 36 months.

RESULTS The cumulative incidence of severe TD was 2.5% after one year, 12.1% after two years, and 22.9% after three years. Individual univariable Cox regression analyses were conducted to identify demographic, psychiatric, motor and pharmacological predictors of severe TD. Results indicated that higher daily doses of neuroleptics at study entry, greater cumulative amounts of prescribed neuroleptic, and greater severity of worsening negative symptoms were predictive of severe TD.

CONCLUSIONS These findings suggest that conventional neuroleptics may be prescribed to older patients only when necessary and at the lowest effective dosage. Additional caution is recommended in patients exhibiting negative symptoms.