AbstractPanic disorder, as defined by the DSM III diagnostic criteria, was diagnosed in 117 probands for whom age of onset ranged from 10 to 59 years, with a mean of 26.6 years. Diagnosis of parents and siblings was based on interviews with the probands, and only those with “definite” panic disorder by the FISC criteria were considered to be affected. The pattern of concordances for panic across different groups of relatives was estimated concurrently by a log‐linear model for binary pedigree data, assuming different values for the cumulative risk. When an adjustment for age was made, based on the age of onset of probands, there was no significant difference between parent‐offspring concordance and sibling concordance. There was a negative, but not significant, concordance between spouse pairs. Assuming the lifetime cumulative risk was 1.9% for males and 4.7% for females, values considered appropriate for this population, our model predicted that the presence of an affected parent or sibling incurs an approximately five times increase in the risk of developing panic disorder. Our model assumes in effect that this risk is multiplied for each further affected relative. Although the common concordance across relationship groups is consistent with a genetic hypothesis, it can also be explained by common family environmental factors. There is a need for further pedigree studies, using twins and relatives, for example, and reliable information on the cumulati