Pathological gambling (PG) is a chronic mental disorder, and patients cannot stop gambling despite severe negative consequences, such as huge debts, job loss, family break-up, and so on. It is said that PG is more prevalent in Japan than in Western countries. However, PG has not received much attention and has even been thought of as a lack of will to stop gambling rather than a mental disorder. PG has been classified under "Impulse-Control Disorders Not Elsewhere Classified," along with compulsive stealing (kleptomania), starting fires (pyromania) and hair-pulling (trichotillomania), but accumulative evidence suggests that PG has many similarities with substance use disorders. Therefore, PG is being proposed to be classified under "Addiction and Related Disorders" in the DSM-5 draft. In this article, we review neuroimaging studies on PG on the basis of 4 dimensions - sensitivity to monetary reward and loss, craving and cue reactivity, impulsivity, and decision-making. In general, PG patients show reduced sensitivity to both monetary reward and loss, increased gamble-related cue reactivity, and increased impulsivity. In contrast, decision-making contains many elements, and hence, future neuroimaging studies on PG should focus on these individual elements. Some efforts have been made to combine molecular neuroimaging (positron emission tomography) with neuroeconomics to investigate the roles of neurotransmitters in altered decision-making in neuropsychiatric disorders. Understanding the molecular mechanism of extreme or impaired decision-making could contribute to the assessment and prevention of drug and gambling addictions and to the development of novel pharmacological therapies for these addictions.