Many people with intellectual disabilities (ID) depend on caregivers for pain identification and pain management decisions. Therefore, the aim was to explore caregivers' experience with pain in Prader-Willi syndrome (PWS), Williams syndrome (WS), and Fragile-X syndrome (FXS). A questionnaire was developed to gather third-party reporting of mainly pain presence, expression, and coping. Questions had single or multiple choice answers and open text fields, without verification of the putative information. The questionnaire was sent digitally to associations and interest groups for the syndromes and healthcare institutions for people with ID. After excluding absent, unknown, or uncertain genetic diagnoses and people without ID, the remaining 243 responses originated by caregivers (90.6% parents) of children and adults with PWS (n = 165), WS (n = 53), and FXS (n = 25) in English, French, Dutch, and German speaking countries. More than half of all respondents reported the presence of known physical conditions that could be painful (58.4%) and pain observed during the past three months (54.3%, of which 70.9% chronic). Results reveal caregivers' barriers in identifying pain (e.g., interpreting pain expression and sensitivity). Respondents cope with pain mainly by seeking (para) medical help and observe both passive and active coping in people with the syndromes. Within limitations of the study's scope and design (e.g., used questionnaire), the results open a discussion about the validity of caregivers's perspective on pain. In-depth analysis in a more representative sample is recommended, as well as solutions for clinical practice such as training and education material about pain.