The objective is to cast light on diagnosis and catastasis, course, and comorbidity as concerned with catatonia in patients with autism spectrum disorders (ASDs) with respect to long-term prospective follow-up. Eleven patients (all male) were enrolled. The mean age and the mean follow-up duration were 27.6 years (standard deviation (SD) 5.5) and 18.7 years (SD 8.7), respectively. The mean IQ was 27 (SD 16.4). Information was garnered from medical case records; current examination and observation of patients, interview of parents, and questionnaires completed by parents or other caretakers. Informed consent was obtained from the parents. Criteria for catatonia in this study were: (1) abrupt stop of movements and maintenance of immobility or bizarre posture beginning in adolescence and early adult life, (2) such a cataleptic state had continued for at least several minutes and appeared many times a day to the point of interfering with daily activities. We described two typical catatonic cases of ASDs. The average onset age was 19 years (SD 6). In all cases, our diagnostic criteria of catatonia evaluating at worse are fully compatible with those of Diagnostic and Statistical Manual of Mental Disorders, 4th ed. (DSM-VI). In 8 out of 11, the onset of catatonia was clearly preceded by the appearance of slowness in movements accompanying the exacerbation of obsessive-compulsive symptoms. Catatonia was also found to have some connection with Tourette syndrome (3 cases), adjustment disorders (N=1), and depressive mood disorders (N=1). In one case, the manifestations of catatonia had to be distinguished from parkinsonism caused by antipsychotics. Catatonia in ASDs seems to be a chronic condition in most cases. However, there were also a few cases in which catatonia repeatedly aggravated over short spans of time. Catatonia in ASDs may be considered an epiphenomenon of ASDs or a manifestation of comorbidity in adolescence or early adulthood.