To investigate the role of "behavioral inhibition to the unfamiliar" as an early temperamental characteristic of children at risk for adult panic disorder and agoraphobia (PDAG), we compared children of parents with PDAG with those from psychiatric comparison groups. Fifty-six children aged 2 to 7 years, matched for age, socioeconomic status, ethnic background, and ordinal position, were blindly evaluated at the Harvard Infant Study laboratory, Cambridge, Mass. The rates of behavioral inhibition in children of probands with PDAG, with or without comorbid major depressive disorder (MDD), were significantly higher than for our comparison group without PDAG. Further, the data suggest a progression of increasing rates of inhibition from the comparison group without MDD (15.4%), to MDD (50.0%), and to comorbid PDAG and MDD (70%) and PDAG (84.6%). In contrast, the rate of behavioral inhibition in children of probands with MDD did not meaningfully differ from the comparison group without MDD. Behavioral inhibition to the unfamiliar, as defined and measured in the previous work of the Harvard Infant Study program, is highly prevalent in the offspring of adults in treatment for PDAG. These children appear to be at risk for distress and disability in childhood and also perhaps for development of psychiatric disorder in later childhood and aulthood.