The purposes of this study were to examine the specific contribution of illegal acts to the diagnostic criteria of pathological gambling, to assess the possibility of differential item functioning across patients' sex and age, and to explore the existence of different clinical phenotypes based on the presence of illegal acts. The sample consisted of 2,155 patients seeking treatment for pathological gambling at the University Hospital of Bellvitge in Barcelona, Spain. The illegal acts item did not show different item functioning, and younger patients presented higher latent means than middle-aged and older patients, whereas no differences were found across sex. This item also showed the lowest discrimination coefficient; its exclusion would maintain satisfactory internal consistency for the remaining 9 symptoms and was poorly related to psychopathology and the severity of the gambling behavior. The relevance of the illegal acts as a diagnostic criterion appears to be limited, and its elimination from the Diagnostic and Statistical Manual for Mental Disorders, 5th edition, seems justified. However, illegal acts have implications for both the clinical and legal domains and contribute to increase the patients' impairment.