Videotapes of autistic children with stereotypies and/or neuroleptic-related dyskinesias were shown to three experienced raters blind to the children's medication treatment status and history, if any, of neuroleptic exposure. Upon observation of the videotapes, stereotypies and neuroleptic-related dyskinesias were not well differentiated from each other. These results emphasize the importance of assessing and documenting baseline abnormal movements before patients receive neuroleptic therapy. Meticulous baseline evaluation, integral to all patient care, is of particular concern in treating patient populations that often show abnormal movements unrelated to neuroleptic exposure. Such movements can be mistaken clinically for neuroleptic-related dyskinesias and, in the absence of baseline data for comparison, can be misdiagnosed as such.