Little is known about Autism Spectrum Disorder (ASD) in persons over age 50. In a retrospective, naturalistic review of 74 individuals aged 30 and older meeting DSM-5 criteria for ASD, the point prevalence of behavioral and neuropsychiatric symptoms (BNPS) declined significantly for 12 of 13 BNPS over a mean of 25 years while many other features of ASD remained stable. GI disorders (68.9%) and seizure disorders (23%) were common, and 25.7% of the sample had a BMI >30. Females were more likely to engage in screaming (p < 0.05) and oppositional behavior (p < 0.05). Current age did not have a significant effect on BNPS prevalence.