This case study describes the development and use of a portable computer program to assist in behavioral treatment of obsessive compulsive disorder. A 58-year-old female with a 37-year history of compulsive checking rituals, who had mild improvement following 36 months of standard behavioral techniques and pharmacotherapy, showed improved compliance with behavioral treatments of exposure and response prevention following use of the portable computer program. Computer records indicated marked reductions in frequency of checking rituals and a 91-week follow-up indicated that treatment effects were maintained at home where the patient had resumed using the laptop computer. She had stopped using the pocket computer outside the home, and there her checking rituals had returned to baseline levels.