Psychometric evaluations were not used in this study. Data from a randomly selected group of 37 officers is reported. Psychiatric assessment was conducted within days of the undercover operation termination; individual and group psychological debriefings were conducted. Over the following 2 years, routine assessment and reviews were conducted at 6-month, 1-year, and 2-year intervals. Ongoing psychological and psychiatric management was provided if required. The police administration rated 41 percent of the agents "very successful" in their undercover duties; another 24 percent were rated "successful", for 35 percent, the police objectives of the operation were achieved. These ratings were based on police operational criteria. The majority of problems encountered during deployment involved police and operational matters rather than health or welfare matters. All the agents endured frequent danger; some were physically assaulted, but none suffered serious injury. Emerging during the training process and enhanced by the "rush" of deployment, exacerbations of narcissistic (concentration of psychological interest upon the self) traits became apparent in the agents. The clinical impression was that moderate rather than minor or severe narcissism correlated with successful operations. No persisting affective or posttraumatic symptoms were recognized during deployment, and no psychotic episodes were provoked. The termination emotional "let-down" and the acknowledgment of their betrayal of their criminal friends was anticipated and universal. Relief, fatigue, and sadness were the predominant clinical observations at this juncture. During the period 1985-91, 16 percent of the undercover agents suffered major psychological or psychiatric sequelae. One officer suffered posttraumatic stress disorder, another a major depressive disorder, and the remaining presented with significant difficulties in regaining their prior police identity and lifestyle. Suggestions for minimizing the risk of psychological deterioration for undercover agents focuses on selection and training. 29 references