PURPOSE. Several studies have reported higher levels of macular pigment (MP) in association with reduced risk for age-related macular degeneration (ARMD), a disease to which there is a genetic predisposition. A classic twin study was performed to determine the heritability of MP in the healthy eye. METHODS. One hundred fifty twin pairs (76 monozygotic [MZ] and 74 dizygotic [DZ]), aged 18 to 50 years, participated. MP optical density was measured psychophysically with hcterochromatic flicker photometry (HFP) and also with an imaging method involving fundus autofluorescence (AF). The covariance of MP within MZ and DZ twin pairs was compared, and genetic modeling techniques were used to determine the relative contributions of genes and environment to the variation in MP. RESULTS. The mean MP optical density, measured using HFP, was 0.43 ± 0.21. Using AF, the mean MP optical density, measured at 1° eccentricity, was 0.28 ± 0.11. MP optical densities correlated more highly in MZ twins than in DZ twins, according to both HFP (MZ: 0.65; DZ: 0.24) and AF (MZ: 0.83; DZ: 0.50). A model combining additive genetic and unique environmental effects provided the best fit and resulted in MP heritability estimates of 0.67 (95% CI, 0.52-0.77) and 0.85 (95% CI, 0.78-0.90) for HFP and AF readings, respectively. CONCLUSIONS. This classic twin study demonstrates that genetic background is an important determinant of MP optical density, reflected in heritability estimates of 0.67 and 0.85 for HFP and AF measures, respectively.