Homicide is frequently associated with mental illness and suicide. The present study is an investigation of all known homicide incidents in Iceland during the past 80 years (1900-1979). There were 45 homicide incidents, involving 52 victims and 47 offenders. One-third of the perpetrators were either psychotic, mentally subnormal, or committed suicide. A further one-third were diagnosed as personality disordered, alcoholic, drug dependent or neurotic. A substantial proportion of the offenders suffered from fairly marked physical disabilities, and the mentally ill were significantly more frequently afflicted by such defects. Over 60% of the offenders and 50% of the victims were under the influence of alcohol at the material time. The findings are generally consistent with those of previous psychiatric studies of homicide.