Background: Recruitment is a widely cited barrier of representative intellectual disability research, yet it is rarely studied. This study aims to document the rates of recruiting children with intellectual disabilities using two methods and discuss the impact of such methods on sample characteristics. Methods: Questionnaire completion rates are compared between (i) participants being approached in child development centre waiting rooms and (ii), one year later, the same participants being invited to take part by phone, email and/or post. Results: The face-to-face recruitment method resulted in a better recruitment rate (58.5% compared to 18.5%) and a larger sample (n = 438) than the telephone/email/post sample (n = 40). It also required less hours of researcher time per completed questionnaire. Conclusions: In-line with previous research, recruitment of participants with intellectual disabilities (or their parents/carers) requires significant time and resources to get a sample of an acceptable size.