Aggressive behavior was documented in a sample of 124 residents on units for the cognitively impaired in four nursing homes over a period of 7 days using the Ryden Aggression Scale. Some form of aggression was found in 86.3% of the residents, with no differences among facility, gender or diagnostic group. Neither mental status nor physical dependency was associated with aggression. The 68.5% who received psychotropic drugs had significantly higher aggression scores. Most incidents of aggression involved response to invasion of personal space and occurred during the day shift.