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The authors investigated whether striatal dopamine D₂ receptor binding characteristics in vivo are similar in men and women and whether there are sex-related differences in the decline in D₂ receptor density due to aging. Striatal D₂ receptor density (B_max), affinity (K_d), and binding potential (B_max/K_d) were measured with positron emission tomography and [¹¹C]raclopride in 54 healthy subjects (33 men and 21 women). Women had generally lower D₂ receptor affinity than men, and this difference was statistically significant in the left striatum. B_max and B_max/K_d tended to decline with age twice as fast in men as in women, but the difference did not reach statistical significance. These results confirm the age-related reduction of D₂ receptor density and binding potential in both sexes in vivo. The lower D₂ receptor affinity suggests an increased endogenous striatal …