A multistage sampling technique was used to select 845 pregnant women from two blocks in Vellore district. Haematological measurement of haemoglobin (Hb) was done on all women and serum ferritin (SF) on a subsample of 445. The prevalence of anaemia (Hb <11 g/dl) was 56.6%, 70.2% and 69.5%, respectively among the first, second and third trimester women. The mean Hb of 10.7 g/dl was significantly higher among the first trimester than among the second and third trimester women, which was less than the recommended value of 11 g/dl. Iron deficiency (SF <12 microg/L) was significantly (P< 0.05) more among the third trimester women than among the first. The high prevalence of anaemia in each trimester in pregnancy indicates the need for iron supplementation as early as possible starting from the fourth month of pregnancy.