Should the combined and predominantly inattentive types of ADHD be considered distinct and unrelated disorders? Not now, at least

The proposal of Milich, Balentine, and Lynam in this issue that the combine d and predominantly inattentive types of attention-deficit/hyperactivity di sorder (ADHD) be considered distinct and unrelated disorders is well-concei ved and important. Given the current state of the empirical literature on t his aspect of the taxonomy of ADHD, however, their proposal can neither be accepted nor rejected at this time. Their proposal should stimulate new res earch that can resolve this issue. Vexing measurement issues that would mak e it difficult to create a stable diagnostic boundary between two such puta tive disorders must be addressed, however, and care must be taken to avoid creating a new diagnostic category that confuses the taxonomy of anxiety an d depression.