Although conception-to-weaning times in dasyurid marsupials are extremely long and neonates very small, little is known about their growth and thermoenergetics. We studied the growth pattern of 'Antechinus stuartii' from birth to after weaning in relation to thermoregulatory capabilities and energetic cost of lactation in the female. Litter size was 1-8 young. Growth rate was slow for age 0-40 days, increased until weaning at about 100 days of age, and then slowed again. At weaning, males were 18% heavier than females (t-test, P<0.001). Energy expenditure of females increased significantly by about 30% during late lactation, compared with early or postlactation. Overall, maternal investment increased with increasing litter size. Total energy expenditure from birth to weaning was 2,373 kJ for small litters (1-3 young) and about 4,580 kJ for large litters (8 young). However, at weaning, young from small litters were about 30% heavier than young from large litters. Ability of young 'A. stuartii' to thermoregulate improved with age. At 60 days age, young were poikilothermic after cold exposure, but by 79 days, physiological thermoregulation was established.