Despite well-documented individual, relational, and health benefits, masturbation has been stigmatized and is understudied compared to partnered sex. In a US nationally representative survey of adults, we aimed to: (1) assess the prevalence and frequency of participants’ prior-year masturbation, (2) describe reasons people give for not masturbating, (3) describe reasons people give for masturbating, and (4) examine the association between masturbation frequency and actual/desired partnered sex frequency in the prior year. Significantly more men than women reported lifetime masturbation, past month masturbation, and greater masturbation frequency. The most frequently endorsed reasons for masturbating related to pleasure, feeling “horny,” stress relief, and relaxation. The most frequently endorsed reasons for not masturbating were lack of interest, being in a committed relationship, conflict with morals or values, or being against one’s religion.