This study aimed to estimate the prevalence of autism-spectrum conditions in Cambridgeshire, UK, using different methods, including the Special Educational Needs (SEN) register and a diagnosis survey. The SEN register reported 83 cases of autism-spectrum conditions, with a prevalence estimate of 94 per 10,000. The diagnosis survey reported 41 cases, with an adjusted prevalence estimate of 99 per 10,000. A total of 11 children were diagnosed with autism-spectrum conditions through screening and assessment, resulting in an overall prevalence estimate of 157 per 10,000, including previously undiagnosed cases. The study highlights the existence of undiagnosed cases and suggests that appropriate services should plan for between 1–2% of the primary school-aged population. The findings are consistent with previous studies, indicating a prevalence of around 1%. However, the study acknowledges limitations, such as low parental response rates and potential biases in reporting diagnoses.This study aimed to estimate the prevalence of autism-spectrum conditions in Cambridgeshire, UK, using different methods, including the Special Educational Needs (SEN) register and a diagnosis survey. The SEN register reported 83 cases of autism-spectrum conditions, with a prevalence estimate of 94 per 10,000. The diagnosis survey reported 41 cases, with an adjusted prevalence estimate of 99 per 10,000. A total of 11 children were diagnosed with autism-spectrum conditions through screening and assessment, resulting in an overall prevalence estimate of 157 per 10,000, including previously undiagnosed cases. The study highlights the existence of undiagnosed cases and suggests that appropriate services should plan for between 1–2% of the primary school-aged population. The findings are consistent with previous studies, indicating a prevalence of around 1%. However, the study acknowledges limitations, such as low parental response rates and potential biases in reporting diagnoses.