Men with hypogonadism tend to have low hemoglobin (HGB) levels. We have investigated a cohort of 36 consecutive male patients with macroprolactinomas to evaluate HGB during presentation and following treatment with cabergoline to suppress prolactin (PRL). Patients' mean age at diagnosis was 48 years, the mean adenoma size measured 31 mm. The median PRL at baseline was 1,969 ng/ml; the mean testosterone level was low, 1.5 ng/ml. PRL had been successfully normalized in all but six men by using cabergoline. Mean baseline HGB at diagnosis was 13.1 gr%. Sixteen patients had HGB ≤ 13 gr%, including 4 men with HGB ≤ 11.5 gr%. In the subgroup of 15 men with very low testosterone (≤ 1 ng/ml), baseline HGB was 12.6 gr% compared with 13.5 gr% in patients with higher testosterone (P < 0.005). In 30 men in whom follow-up CBC data were available, mean baseline HGB increased from 13.2 to 13.9 gr% following PRL suppression by cabergoline. Baseline HGB levels inversely correlated with tumor size, reaching levels of 13.7 gr% in 10 men with macroprolactinomas of 10-20 mm in size, 13.0 gr% in 18 subjects with macroadenomas of 21-40 mm, and 12.4 gr% in 7 patients with giant prolactinomas (>40 mm). In 22 men with normal follow-up testosterone, current HGB levels measured 14.5 gr%, but only 12.8 gr% in 9 men with current low testosterone (P < 0.0005). In men with macroprolactinomas, anemia is common. It is associated with hypogonadism and tumor size, and improves following treatment that normalizes PRL and increases testosterone.