The relation between OCPD and OCD has been controversial. Historically, many authors theorized that the two disorders were considered part of the same spectrum of illness. Evidence is growing, however, that the disorders are not part of a continuum. Others reported that OCPD was a common and necessary premorbid condition before the development of OCD. It has more recently been suggested that OCPD may develop as an adaptation to illness in some patients with OCD. At present, the disorders are believed to be separate and distinct. Baer et al. (1990) reported that OCPD was present in only 6% of OCD patients. More recently, Bejerot et al. (1998) studied 36 OCD patients and reported that 36% had OCPD. In a study of 277 patients, Diaferia et al. found that OCPD was significantly more common in patients with OCD than in patients with panic disorder and major depression. Rosen and Tallis found obsessional symptoms to be more likely associated with traits of OCPD than with traits associated with other personality disorders.

In differentiating OCD from OCPD, some authors emphasize the tendency for OCPD patients’ traits to be ego-syntonic, in contrast to the ego-dystonic and intrusive symptoms of the patient with OCD. Distinct obsessional thoughts and the need to perform rituals are considered the hallmarks of OCD. This distinction does have limitations. In some cases of OCD, for example, when symmetry or exactness is required, the symptoms may be experienced by the patient as very syntonic.

The more chronic and persistent symptomatology of OCPD also may help to distinguish the two disorders. OCD patients have been shown in numerous studies to respond favorably to behavioral therapies and to serotonergic medications. Individuals with OCPD also may be clearly differentiated from those with obsessive-compulsive traits by the severity of their symptoms. The empirical validity of OCPD has been established in relation to both OCD and obsessional personality traits.