BACKGROUND The provision of a thermoneutral environment is an essential component of the immediate and longer term care of newborn infants. A variety of methods are currently employed including incubators and open-care systems, with or without modifications such as heat shields and plastic wrap. The system used must allow ready access to the infant but should also minimise alterations in the immediate environment. OBJECTIVE To assess the effects of radiant warmers versus incubators on neonatal fluid and electrolyte balance, morbidity and mortality. METHODS The standard search strategy of the Cochrane Neonatal Review Group was used. This included searches of electronic databases: Oxford Database of Perinatal Trials, Cochrane Controlled Trials Register (Cochrane Library Issue 4 2001), MEDLINE (1966 -2001), and CINAHL (1982-2001). METHODS Randomised or quasi-randomised trials in which radiant warmers were compared to incubators in a neonatal population. METHODS Independent data extraction and quality assessment of included trials was conducted by the authors. Data were analysed using relative risk (RR) and weighted mean difference (WMD). Results are presented with 95% confidence intervals. Meta-analysis was undertaken using a fixed effect model. RESULTS Eight studies are included in this review; six employed a crossover design. In the overall comparison of radiant warmers vs incubators, radiant warmers caused a statistically significant increase in insensible water loss (IWL) [WMD 0.94g/Kg/day (95% CI 0.47, 1.41)] and a trend towards increased oxygen consumption which was not statistically significant [WMD 0.27mL/kg/min (95% CI -0.09, 0.63)]. Due to small numbers, effects on important clinical outcomes could not be adequately assessed. A comparison of radiant warmers with heat shields vs incubators without heat shields showed a trend for increased IWL in the radiant warmer group, which was not statistically significant. No difference was shown in oxygen consumption. CONCLUSIONS Radiant warmers result in increased IWL compared to incubators. This needs to be taken into account when calculating daily fluid requirements. The results of this review do not provide sufficient evidence concerning effects on important outcomes to guide clinical practice. Further randomised controlled trials are required to assess the effects of radiant warmers versus incubators in neonatal care on important short and long term outcomes, with particular attention to extremely low birthweight infants in the early neonatal period.