This study investigated whether children with autism spectrum disorders (ASD) can learn vocabulary from linguistic context. Thirty-five children with ASD (18 with age-appropriate structural language; 17 with language impairment [ALI]) and 29 typically developing peers were taught 20 Science words. Half were presented in linguistic context from which meaning could be inferred, whilst half were accompanied by an explicit definition. Children with ASD were able to learn from context. Condition did not influence phonological learning, but receptive semantic knowledge was greatest in the context condition, and expressive semantic knowledge greatest in the definitional condition. The ALI group learnt less than their peers. This suggests that at least some vocabulary should be taught explicitly, and children with ALI may need additional tuition.