The parents of 80% (41 of 51) of preschoolers with cystic fibrosis (CF) diagnosed at least 1 year prior to the study and attending the Hospital for Sick Children (HSC) CF Clinic completed the Problem Inventory (PINV), Preschool Behavior Questionnaire (PBQ) and Family Assessment Measure (FAM). The mean age of the CF children was 3.7 years. Parents of a control group of 31 healthy daycare children with a mean age of 3.6 years completed the same questionnaires. Parents of healthy preschoolers reported more child-related problems for 2-5 year olds than did parents of CF children (P less than 0.001) suggesting that parents who have confronted the CF diagnosis go on to minimize the normal stresses of the developmental period. Considerable agreement was seen between PINV scores for mothers and fathers in each group, revealing that parents in a given family perceive similarly the impact their child has upon them. The mean PBQ for CF preschoolers was not significantly different from that of the control group, although there was some tendency toward hostile aggressive behavior in the CF group. Surprisingly, total FAM scores of all samples showed no significant differences with the exception of a better total FAM score for fathers of CF children when compared to control fathers revealing that the CF family is not, during the early years of relative health stability, adversely affected. Two subscales were significantly elevated, social desirability (for CF mothers and fathers) and denial (for CF mothers only), describing an important response style which may enhance mastery of long-term stress.(ABSTRACT TRUNCATED AT 250 WORDS)