This study estimated differences by ethnicity in the diagnoses assigned prior to the diagnosis of autism. In this sample of 406 Medicaid-eligible children, African-Americans were 2.6 times less likely than white children to receive an autism diagnosis on their first specialty care visit. Among children who did not receive an autism diagnosis on their first visit, ADHD was the most common diagnosis. African-American children were 5.1 times more likely than white children to receive a diagnosis of adjustment disorder than of ADHD, and 2.4 times more likely to receive a diagnosis of conduct disorder than of ADHD. Differences in diagnostic patterns by ethnicity suggest possible variations in parents’ descriptions of symptoms, clinician interpretations and expectations, or symptom presentation.