In non-human animal research, studies comparing socially monogamous and promiscuous species of voles (Microtus) have identified some key neural differences related to monogamy and non-monogamy. Specifically, densities of the vasopressin V1a receptor and dopamine D2 receptors in subcortical reward-related and limbic areas of the brain have been linked to monogamous behavior in prairie voles (Microtus ochrogaster). Similar brain areas have been shown to be correlated with feelings of romantic love in monogamously pair-bonded humans. Humans vary in the degree to which they engage in (non-)monogamous behaviors. The present study examined the differences in neural activation in response to sexual and romantic stimuli in monogamous (n = 10) and non-monogamous (n = 10) men. Results indicated that monogamous men showed more reward-related neural activity when viewing romantic pictures compared to non-monogamous men. Areas with increased activation for monogamous men were all in the right hemisphere and included the thalamus, accumbens, striatum, pallidum, insula, and orbitofrontal cortex. There were no significant differences between groups in activation to sexual stimuli. These results demonstrate that the neural processing of romantic images is different for monogamous and non-monogamous men. There is some overlap in the neural areas showing increased activation in monogamous men in the present study and the neural areas that show differences in the vole models of monogamy and affiliation. Future research will be needed to clarify whether similar factors are contributing to the neural differences seen in monogamous and non-monogamous humans and voles.