OBJECTIVE Although HbA(1c) is known to be affected by the lifespan of erythrocytes, any association of erythrocyte indices with HbA(1c) in subjects without anaemia is poorly understood. Pre-menopausal women may be relatively iron deficient because of menstruation. In this study, we examined the relationship between HbA(1c) and erythrocyte indices in pre- and post-menopausal women. METHODS We determined HbA(1c), red blood cell (RBC) count, haematocrit, haemoglobin, mean corpuscular volume (MCV) and mean corpuscular haemoglobin (MCH) in 423 women with normal glucose tolerance who had undergone health checks. In addition, age at menopause was recorded in post-menopausal subjects. RESULTS RBC counts of the 180 pre-menopausal women were positively associated with HbA(1c), whereas haemoglobin, MCV and MCH showed a negative association. In contrast, no significant association of any indices with HbA(1c) was detected in the 243 post-menopausal women. Stepwise multivariate regression analysis in the pre-menopausal women identified fasting plasma glucose and age as positively associated and MCH as negatively associated with HbA(1c), regardless of whether or not these pre-menopausal women were anaemic. CONCLUSIONS Erythrocyte indices are associated with HbA(1c), independently of plasma glucose levels, in pre-menopausal women even when they are not anaemic. This should be appreciated when interpreting HbA(1c) in pre-menopausal patients with diabetes.