Importance: Pornography consumption is highly prevalent, particularly among young adult males. For some individuals, problematic pornography use (PPU) is a reason for seeking treatment. Despite the pervasiveness of pornography, PPU appears under-investigated and basic questions remain unanswered. Objective: To investigate the neural mechanisms underlying PPU in men. Design and participants: Using functional magnetic resonance imaging (fMRI), we examined brain reactivity towards erotic and monetary stimuli, disentangling cue-related 'wanting' from reward-related 'liking' among 28 heterosexual males seeking treatment for PPU and 24 heterosexual males without PPU. Subjects could have won either erotic pictures or monetary gains in an incentive delay task, where rewards were preceded by predictive cues. Main outcome measures: BOLD signal activity relating to responses to erotic and monetary cue processing and measured during fMRI was analyzed and examined with respect to self-reported data on sexual activity collected over the 2 preceding months. Results: Men with and without PPU differed in brain reactions to cues predicting erotic pictures, but not in reactions to erotic pictures themselves, consistent with the incentive salience theory of addictions. PPU subjects showed increased activation of a brain reward region (the ventral striatum) specifically for cues predicting erotic pictures but not for cues predicting monetary gains. This brain activation was accompanied by increased behavioral motivation to view erotic images (higher 'wanting'). Ventral striatal reactivity for cues predicting erotic pictures was significantly related to the severity of PPU, amount of pornography use per week and number of weekly masturbations. Conclusions and relevance: Our findings suggest that like in substance-use and gambling disorders the neural and behavioral mechanisms linked to anticipatory processing of cues relate importantly to clinically relevant features of PPU. These findings suggest that PPU may represent a behavioral addiction and that interventions helpful in targeting behavioral and substance addictions warrant consideration for adaptation and use in helping men with PPU.