We examined whether the link between intelligence and musical expertise is better explained by formal music lessons or music aptitude. Musically trained and untrained adults completed tests of nonverbal intelligence (Raven's Advanced Progressive Matrices) and music aptitude (Musical Ear Test). They also provided information about their history of music lessons and socioeconomic status (SES). Duration of music training was associated positively with SES (mother's education), nonverbal intelligence, melody aptitude, and rhythm aptitude. Intelligence and music aptitude were also positively associated. The association between music training and intelligence remained evident after controlling for SES, but it disappeared after controlling for music aptitude. By contrast, music aptitude had a strong correlation with intelligence even after accounting for music training and SES. Thus, the association between music training and intelligence may arise because high-functioning individuals are more likely than other individuals to have good aptitude for music and to take music lessons.