This paper compares attention deficit disorder (ADD) with hyperactivity (ADDH) and without hyperactivity (ADDWO). The literature is outlined, revealing the areas of possible differences to be not only the core symptoms, but also associated conduct and emotional symptoms, social relations functioning, learning, medical disorders, family history, and course and outcome of the disorder. Empirical data are presented comparing age and sex matched groups of children from a speech/language clinic sample with ADDH (N = 40) and ADDWO (N = 40). Although the methods of the present study are different from those of previous studies, they nonetheless support a number of previous findings, and, further, give support to the external validity of the ADDWO diagnostic category.