Violent incidents in psychiatric institutions have been the focus of much study over the past few decades. But there has been little work looking at similar incidents in child and adolescent units. The authors set out to examine whether some of the patterns observed in adult populations are true of adolescent groups. The Gardener Unit was considered appropriate in light of reports of a higher frequency of assaultative behaviour among younger clients and because of the nature of problems presented by clients needing a secure environment. All violent incidents are automatically recorded. The violent incident register was examined between 1 June 1991 and 1 June 1992 and the information cross-checked with case notes and nursing reports. Demographic details, etc. were obtained from case notes. The results indicated a slightly higher daily incident rate than adult studies. At least half of the population were involved in some form of violent episode over the 12-month period. The majority of incidents were minor in nature. Nursing staff were the most frequent targets, although females showed an excess of inwardly directed aggression (self harm). A prior history of violent behaviour did not serve as a realistic predictor of frequency of violent incidents in this study. With increasing concern regarding the care of this disturbed group of young people, it was felt important to look closely at the nature of and handling of violent incidents on this unit. A second paper will consider in detail how these incidents were dealt with.