OBJECTIVES: To determine the effects on weight gain and temperature control of transferring preterm infants from incubators to open cots at a weight of 1600 g versus a weight of 1800 g. DESIGN: Randomised controlled trial. SETTING: One tertiary and two regional neonatal units in public hospitals in Queensland, Australia. PARTICIPANTS: 182 preterm infants born with a birth weight less than 1600 g, who were at least 48 h old; had not required ventilation or continuous positive airways pressure within the last 48 h; were medically stable with no oxygen requirement, or significant apnoea or bradycardia; did not require phototherapy; and were enterally fed with an intake (breast milk/formula) of at least 60 ml/kg/day. INTERVENTIONS: Transfer into an open cot at 1600 or 1800 g. MAIN OUTCOME MEASURES: The primary outcomes were temperature stability and average daily weight gain over the first 14 days following transfer to an open cot. RESULTS: 90 infants in the 1600 g group and 92 infants in the 1800 g group were included in the analysis. Over the first 72 h, more infants in the 1800 g group had temperatures <36.4°C than the 1600 g group (p=0.03). From post-transfer to discharge, the 1600 g group had more temperatures >37.1°C (p=0.02). Average daily weight gain in the 1600 g group was 17.07 (SD±4.5) g/kg/day and in the 1800 g group, 13.97 (SD±4.7) g/kg/day (p=<0.001). CONCLUSIONS: Medically stable, preterm infants can be transferred to open cots at a birth weight of 1600 g without any significant adverse effects on temperature stability or weight gain. TRIAL REGISTRATION: ACTRN12606000518561 (http://www.anzctr.org.au).