During pregnancy, the metabolic rate of females may increase above basal levels to support metabolically active tissues and developing embryos. In mammals, this energetic cost of supporting the pregnancy (MCP) is an important component of reproductive effort, but less is known about the magnitude of this cost in ectothermic vertebrates. We estimated the metabolic cost of supporting pregnancy in a tropical viviparous snake, the Northern Death Adder, Acanthophis praelongus. We measured the metabolic rates of non-gravid and gravid females throughout gestation and following parturition. We also measured the oxygen consumption of a sample of neonates from each clutch within 24 h of birth. The metabolic rate of gravid females rose slowly during pregnancy, but was significantly elevated during the last three weeks of gestation. Considering the late term metabolism of gravid females as 100%, then the baseline metabolism of female Death Adders represented 36.6%, embryo metabolism accounted for 37.0%, and the cost of supporting the pregnancy was 26.4% of the total metabolic rate. Neonate metabolism during the first 24 h of birth was 2.9 times higher than the estimate for embryo metabolism. Thus, our results do not support the assumption that the metabolism of embryos (prior to birth) and neonates is similar in this species. Although gravid female Death Adders maintain high and constant body temperatures during late gestation, the energetic cost of supporting the pregnancy is only a minor component of the total reproductive effort for females of this species.