: The mu-opioid antagonist nalmefene (18 mg per day) was administered in the treatment of a heterosexual male with internet pornography addiction. The patient had no other co-addictions or psychiatric comorbidities, allowing a direct measurement for the effectiveness of nalmefene on internet pornography addiction. Over a period of 72 weeks and an assessment frequency between 1 and 18 weeks, self-monitoring assessments of craving and pornography consumption were collected on different craving and obsessive-compulsive scales. Results indicate that nalmefene impressively decreased addictive symptoms. Importantly, the patient-induced discontinuation of nalmefene led to an immediate increase of craving scores and addictive behavior, which dropped again after restarting the medication. The patient has been in complete remission of symptoms for over a year under our supervision, and for further 2 years after that according to his account. Therefore, nalmefene seems to be a useful adjunction for patients with internet pornography addiction.