OBJECTIVE To examine the relation between parent expectations for antibiotics, parent communication behaviors, and physicians' perceptions of parent expectations for antibiotics. METHODS A nested cross-sectional study with parallel measures of parents presenting children for acute respiratory infections (previsit) and physicians (postvisit) and audiotaping of the encounters. METHODS Ten physicians in 2 private pediatric practices (1 community-based and 1 university-based) and a consecutive sample of 306 eligible parents (response rate, 86%) who were attending sick visits for their children between October 1996 and March 1997. METHODS Communication behaviors used by parents expecting antibiotics and physicians' perceptions of parents' expectations. RESULTS Parents' use of "candidate diagnoses" during problem presentation increased the likelihood that physicians would perceive parents as expecting antibiotics (from 29% to 47%; P=.04), as did parents' use of "resistance to the diagnosis" (an increase from 7% to 20%). In the multivariate model, parents' use of candidate diagnoses increased the odds that a doctor would perceive a parental expectation for antibiotics by more than 5 times (odds ratio, 5.23; 95% confidence interval, 3.74-7.31; Plt.001), and parents' use of resistance to a viral diagnosis increased these odds by nearly 3 times (odds ratio, 2.73; 95% confidence interval, 1.97-3.79; Plt.001). CONCLUSIONS Parents perceived as expecting antibiotics may be seeking reassurance that their child is not seriously ill or that they were correct to obtain medical care. Physicians were significantly more likely to perceive parents as expecting antibiotics if they used certain communication behaviors. This study revealed an incongruity between parents' reported expectations, their communication behaviors, and physicians' perceptions of parents' expectations.