OBJECTIVES: To examine the gender-specific distribution of haemoglobin (Hb) and the World Health Organization (WHO) criteria for anaemia compared with the 2.5 percentile for Hb. METHODS: A population-based study from Tromsø, Northern Norway. All inhabitants above 24 yr were invited. In total, 26 530 (75%) had their Hb analysed. RESULTS: The 2.5-97.5 percentile of Hb was 129-166 and 114-152 g/L for all men and women, respectively. In men, mean Hb decreased from 148 to 137 g/L between 55-64 and 85+ yr. In women, mean Hb increased from 132 to 137 g/L between 35-44 and 65-74 yr and then decreased to 131 g/L among the oldest. Using the WHO criteria for anaemia (Hb: