Autism spectrum disorder (ASD) is a neurodevelopmental disorder with a global prevalence of approximately 1%. This review summarises new evidence of association between bipolar disorder (BD) and ASD. The mood episodes of BD can present atypically in people with ASD, potentially leading to misdiagnosis. Anamnesis regarding family history of affective disorders as well as previous mood episode is important among people with ASD to capture the BD diagnosis. Precaution with SSRI-treatment among people with ASD is crucial as the treatment can potentially trigger a mood episode of an underlying BD.