Four hundred twenty-nine pregnant women who had back pain before pregnancy and 375 pregnant women with no previous back pain were followed at regular intervals from the 12th week of pregnancy until delivery; back-pain complaints were recorded. Overall, back pain occurred twice as often in the group with a back-pain history (period prevalence) (P< 0.001). The point prevalence of back pain in weeks 12, 24, 30, and 36 was three times higher in the group who had had back pain before pregnancy indicating that pain was not only more prevalent but also lasted longer in that group. Women who had been pregnant previously tended to have an increased risk of back pain, and there was a statistically significant correlation between multiparity and longer periods of back pain (P< 0.001). Young age increased the risk of back pain (P< 0.001). Pain intensity was higher in the younger women during the first part of their pregnancies but not later on (P< 0.05).