The prevalence and characteristics of back pain were recorded in 855 women on nine occasions during pregnancy from the 12th to the 36th week of gestation. Data on delivery and pain relief were recorded. At 12 months post partum the women were reassessed regarding the presence of back pain. Women with a history of back pain had more intense pain (p less than 0.05). No correlation was observed between back pain (a) during pregnancy and (b) after pregnancy and delivery, nor between (a) the need for pain relief in labor and (b) birthweight, length and Apgar score. Back pain usually disappeared in the first 6 months post partum, except in women with recurrent back pain from previous pregnancies. Eighty-two percent of these women continued to have back pain at 18 months post partum, compared with 45% of all other multi-parous women (p less than 0.001).