This case study reports the clinical and physiological changes of a 33 year old elite marathoner undertaking intensive endurance training during and following a twin pregnancy. Prior to conception, the subject ran 155 km x week(-1) at an intensity equivalent to 140-180 b x min(-1) which following consultation decreased to 107 +/- 19 km x week(-1) at an intensity equivalent to 130-140 b x min(-1) during pregnancy. Physical exercise ceased 3 days prior to an elective Caesarean section following a 36 week gestation period and recommenced 8 days following the birth of healthy twins. Medical assessments conducted ante/post partum indicated that both the twins and mother were healthy. A field based test demonstrated that running velocity at a steady state HR of 140 b x min(-1), 150 b x min(-1) and 160 b x min(-1) decreased by 20%, 15% and 13% respectively between weeks 1 and 32 antepartum. Whole blood lactate ([La-]B), oxygen uptake (VO2), ventilatory equivalent for oxygen (V(E)/VO2), HR and Borg rating of perceived exertion (RPE) increased during a laboratory-based submaximal treadmill test at 29 weeks antepartum in comparison to a test conducted 10 weeks post partum. These data clearly demonstrate that it is possible for an elite endurance athlete to maintain a high level of cardiovascular fitness during pregnancy with no apparent adverse effects on maternal or foetal health. This will facilitate an earlier return to international competition.