Mentally retarded adults' ability to express facial emotions of happiness, sadness, anger, and fear was investigated. Photographs of facial emotional expressions posed by 52 retarded adults were judged by familiar and unfamiliar nonretarded adults. Happiness and sadness were accurately posed most often. The ability of retarded adults to encode facial emotional expressions was found to be significantly correlated with assessments of interpersonal competence provided by work supervisors in a sheltered workshop setting. Implications for nonverbal social/emotional assessment, nonverbal interpersonal skills training, and future research are discussed. Includes 28 references. (JDD)