Contemporary cognitive models of obsessive-compulsive disorder (OCD) assume that clinical obsessions evolve from some modalities of intrusive thoughts (ITs) that are experienced by the vast majority of the population. These approaches also consider that the differences between "abnormal" obsessions and "normal" ITs rely on quantitative parameters rather than qualitative. The present paper examines the frequency, contents, emotional impact, consequences, cognitive appraisals and control strategies associated with clinical obsessions in a group of 31 OCD patients compared with the obsession-relevant ITs in three control groups: 22 depressed patients, 31 non-obsessive anxious patients, and 30 non-clinical community subjects. Between-group differences indicated that the ITs frequency, the unpleasantness and uncontrollability of having the IT, and the avoidance of thought triggers obtained the highest effect sizes, and they were specific to OCD patients. Moreover, two dysfunctional appraisals (worry that the thought will come true, and the importance of controlling thoughts) were specific to OCD patients. The OCD and depressed patients shared some dysfunctional appraisals about their most disturbing obsession or IT (guilt, unacceptability, likelihood thought would come true, danger, and responsibility for having the IT), whereas the non-obsessive anxious were nearer to the non-clinical participants than to the other two groups of patients. The OCD patients showed an increased use of thought control strategies, with overt neutralizing, thought suppression, and searching for reassurance being highly specific to this group.