The purpose of this study was to assess what role psychological and social factors play in predicting the participation of elderly people in a social activation program. Furthermore, the study evaluated the importance of such factors in improving subjects’ moods and decreasing feelings of loneliness. Over a six-month period, a social activation program was conducted in a senior citizen apartment bulding in Stockholm, Sweden. A group of 30 residents from one floor of the building, the experimental group, received the program while a control group of 30 residents from another floor did not. Medical, social, psychological, and behavioral assessments were made immediately before, three months after, and six months after the beginning of the program. Results were that the activity level had increased threefold in the experimental group. Experimental group subjects who initially had a low social activity level and higher scores on the internal-locus-of-control scale had the highest rate of increase in their social activity level. Subjects in the experimental group who initially had a low social activity level, were single or bereaved, scored low on the neuroticism scale, or desired a low level of internal control showed the greatest improvement in mood. Feelings of loneliness decreased the most among those in the experimental group who had a stronger internal locus of control and scored high on pessimistic feelings. Because the program benefited those subjects who initially were the most passive and isolated, it is concluded that gerontic occupational therapy plays an important role in preventing unnecessary social isolation in institutional living.