Background. This study was undertaken to examine the relationship between anxiety co-morbidity and age of onset of panic disorder.

Methods. Age of onset of panic disorder and co-morbid anxiety disorders were assessed among 201 panic disorder probands with childhood separation anxiety disorder, obsessive–compulsive disorder, obsessive–compulsive symptoms, social phobia and specific phobia as part of a clinician-administered lifetime diagnostic interview. A generalized linear model was used to test the association between each anxiety co-morbidity and age of panic disorder onset while simultaneously controlling for the potential confounding effects of sociodemographic characteristics and other psychiatric co-morbidity.

Results. Earlier onset of panic disorder was found in patients with co-morbid obsessive–compulsive disorder, obsessive–compulsive symptoms and separation anxiety disorder, but not simple phobia or social phobia. Patients with both childhood separation anxiety disorder and obsessive–compulsive disorder had an even earlier panic onset than those with either childhood separation anxiety disorder or obsessive–compulsive disorder.

Conclusions. The association between anxiety co-morbidity and earlier onset of panic disorder is specific to obsessive–compulsive disorder and childhood separation anxiety disorder.