The influence of a behavioural family treatment on parental communication deviance (CD) was investigated in a longitudinal treatment study. Subjects were the parents of young patients with recent-onset schizophrenia or related disorders. Parents and patients were randomly assigned to one of two treatment conditions: individual out-patient treatment or a combination of individual out-patient and family treatment. Parental CD was assessed with the Thematic Apperception Test (TAT) both at the start of the out-patient treatment and after completion of treatment 1 year later. Most families had high levels of CD, a finding which is in agreement with previous CD studies. These high CD levels remained stable over the 12-month period. Family treatment was not effective in influencing the level of CD. The findings suggest that high CD is a stable trait-marker of parents, and they support the notion that high levels of CD may precede the onset of serious psychotic disorders. Studies with more chronic patients are needed to replicate the findings.