Thirty-five outpatients (25 women, 10 men) with a DSM-III-R principal diagnosis of OCD accepted exposure treatment at a psychiatric outpatient clinic. They were randomly assigned to one of two individual treatments for a 6-week exposure therapy treatment based on a treatment manual or to a 6-week waiting list condition. The 12 patients assigned to the waiting list were subsequently randomly assigned to one of the active treatments. Both treatment groups received in vivo or imaginal exposure in each of the 10 twice-weekly treatment sessions held after two assessment sessions. One group (n=16) received cognitive therapy interventions for comorbidity problems or to alter beliefs underlying patients' OCD. The other group (n=19) received relaxation training as an attention placebo control. Both groups received relapse prevention follow-up contacts. Twenty-seven patients completed intensive treatment. Both treatments overall showed satisfactory levels of clinical improvement and large effect sizes. ANCOVAS for treatment completers showed non-significantly lower levels of OCD symptoms, depression and state anxiety in the treatment condition that did not include cognitive interventions. The patients receiving additional cognitive therapy showed significantly lesser dropout than those in the other treatment condition, but there were no significant differences in the intention-to-treat analyses.