It has been suggested that symptoms of panic disorder may be significantly affected by seasonal factors including weather changes, although few studies have explored the issue. The purpose of the present paper was to investigate clinical data to examine sensitivity of panic disorder patients to seasonal changes and seasonal fluctuation of panic disorder symptoms. A self-rating questionnaire consisting of the Seasonal Pattern Assessment Questionnaire (SPAQ) and additional self-rating questions were analyzed in 146 Japanese patients (50 male, 96 female) with panic disorder (DSM-IV) at an outpatient clinic for anxiety disorder. The average of the Global Seasonality Scores (GSS) was 12.5+/-4.7 and 25.3% of the patients were suggested to suffer from seasonal affective disorder, according to the GSS. Frequency of the panic attack was found to fluctuate seasonally, with peaks in August and December (P=0.005 and 0.01, chi2 test). The present results indicate that panic disorder patients may be more sensitive to seasonal and meteorological factors than the general population and become more fragile in a specific season or months. This might assist in the development of preventive measures for the frequent recurrence of symptoms in panic disorder.