The prevention of preterm birth should be one of the major aims of antenatal care. Unfortunately, identification of women who will subsequently deliver preterm is imprecise. Prevention is also difficult. Surgical prevention with cerclage may help a proportion of women. Medical prevention is currently limited to the identification and treatment of bacterial vaginosis, although recent studies have suggested that progesterone prophylaxis may be helpful in some women. Confirmation of efficacy and safety is required before progesterone is introduced as long-term prophylaxis for all women at high risk. The optimal medical treatment (rather than prevention) of threatened preterm labour is controversial. Tocolysis is generally accepted to improve neonatal outcome although this has never been convincingly demonstrated in appropriate trials. Antibiotics confer benefit in the presence of ruptured membranes but are not indicated in uncomplicated preterm labour. In future, it may be possible to identify a subgroup of women in preterm labour with intact membranes who will benefit from tocolysis. The choice of first-line tocolytic therapy is currently debated but atosiban or nifedipine are suggested in current UK guidelines. A direct comparison of these drugs is required in a clinical trial. Although indirect comparisons have been made, these are difficult to interpret due to methodological differences. Each of these drugs have their advocates. Nifedipine has been reported to delay delivery and improve outcome but there are inconsistencies in the clinical trials. Atosiban is also reported to delay delivery and is well tolerated but improved neonatal outcome may have been hidden in clinical trials due to the requirement for rescue tocolysis.