This study was undertaken to investigate the authors' clinical impression that there are significant differences between the male and female insanity acquittees in Colorado, and that these differences result in significantly different treatment needs. The study sample included 149 patients: 112 men and 37 women committed to the Colorado Mental Health Institute at Pueblo as not guilty by reason of insanity (NGRI). Data were collected from a computerized data system and from chart reviews. The study provides descriptive data regarding demographic, legal, and mental health parameters of these acquittees. Demographic items included prior history of incarceration, age at first arrest, type of NGRI crime committed, and severity of NGRI crime. Mental health variables included prior psychiatric hospitalization history of suicide attempts, substance abuse history, inpatient substance abuse treatment history, diagnoses, escape history and length of stay. Percentages of male and female subjects were calculated for those variables with discrete categories. Means and medians were calculated for continuous variables. Results indicate that women are significantly more likely to be given a diagnosis of mood disorder or borderline personality disorder, are significantly older than men at the time of commitment, and are statistically more likely to have committed a single violent crime than men. Men were found to have a significantly higher rate of prior and current substance abuse, a significantly higher rate of antisocial personality disorder, a significantly greater history of violent crime prior to the NGRI offense, and arrests beginning at a significantly younger age than women. Despite the higher severity of crime rating for women, their length of stay was significantly shorter than for men. The implications of the findings with regard to different treatment needs are discussed, and the findings are compared to four other studies addressing female versus male insanity acquittees in other states.