Introduction: Individuals with intellectual disabilities (ID) are at heightened risk of behavioral problems. Methods: This study investigated differences in the severity of challenging behaviors (CBs) among individuals with IDs at varying life stages. Data were collected from parents' retrospective interviews. Surveys were completed by 47 parents whose child with IDs was 19 years or older and had made use of welfare services for individuals who exhibit CBs. Results: The final study sample consisted of 28 parents. Findings showed that: (a) parents gave the lowest total scores for severity of CBs for their adult children when at the pre-school stage compared to other stages (elementary school, junior high school, high school, and post-high school), (b) differences between life stages appear to depend on the type of CB, and (c) the most common CB recorded for children between 0 and 2 years old was extreme hyperactivity, followed by severe sleep disturbances. Conclusions: The results of the study show that domain ratings for stereotypic/restricted behaviors, sleep disturbance problems, feeding problems, and problems with elimination often remain stable throughout the life stages. Moreover, parents frequently reported that CBs often occurred in children aged 0-2 years.