Abnormal illness behavior, such as hypochondriacal attitude and inappropriate treatment-seeking, has been associated with various psychiatric disorders in which patients tend to abuse medical services and seek inappropriate treatment in general practice clinics rather than psychiatric clinics. However, the relationship between illness behavior and psychiatric disorders in Japan is yet to be elucidated. We examined the abnormal illness behavior of 243 patients who visited the outpatient department of psychiatry at Saga Medical School Hospital, Saga, Japan, using a Japanese version of the Illness Behavior Questionnaire (IBQ). Multivariate analysis indicated significant association between some of the IBQ scale scores and age, sex and employment status. Patients with anxiety disorder scored higher on five of the seven IBQ scales compared with patients with another major disorder (mood disorder, schizophrenia or somatoform disorder). When compared with the IBQ scale scores reported in Australian patients in a psychiatric hospital, most of the IBQ scale scores differed significantly in our patients; a higher score among Japanese patients on the general hypochondriasis scale was most prominent. A similar trend in IBQ scale scores was also noted among Japanese patients visiting the hospital's general medicine clinic in comparison with Australian patients visiting a general practice clinic. Japanese patients with anxiety disorder may display the most salient abnormal illness behaviors among patients with psychiatric disorders. Sociocultural background may contribute to the characteristic abnormal illness behaviors of Japanese patients.