Hand mouthing (HM) is a chronic problem in many individuals with intellectual disabilities. Although the prevalence of mouthing has been estimated, data on the frequency, severity, or functions of the behavior were not included. In Study 1, we examined the prevalence and risk of HM. Results obtained from interviews showed that the prevalence of HM in two institutional samples (N = 802) was 12.7%, whereas direct observation yielded a lower estimate of prevalence (8%). Moreover, a large proportion of observed HM (39.1%) was self-injurious in nature. In Study 2, we used modified functional analyses (FAs) to examine the HM of 64 individuals. Results indicated that maintenance by automatic reinforcement accounted for 98.4% of the cases (all but one case). In Study 3, we implemented a progressive series of interventions for HM exhibited by 14 individuals. The following interventions were implemented in sequential order: (a) noncontingent reinforcement (NCR, effective with 6 subjects), (b) either NCR plus differential reinforcement of alternative behavior (DRA) plus response blocking (effective with 5 subjects) or NCR plus response blocking only (effective with 2 subjects), and (c) NCR plus brief manual restraint (effective with 1 subject).