This paper empirically revisits the impact of multiculturalism (as proxied by indices of birthplace diversity and polarization among immigrants, or by epidemiological terms) on the macroeconomic performance of US states over the 1960-2010 period. We test for skill-specific effects of multiculturalism, controlling for standard growth regressors and a variety of fixed effects, and accounting for the age of entry and legal status of immigrants. To identify causation, we compare various instrumentation strategies used in the existing literature. We provide converging and robust evidence of a positive and significant effect of diversity among college-educated immigrants on GDP per capita. Overall, a 10% increase in high-skilled diversity raises GDP per capita by 6.2%. On the contrary, diversity among less educated immigrants has insignificant effects. Also, we find no evidence of a quadratic effect or a contamination by economic conditions in poor countries.