Aims/hypothesis The aim of the study was to assess the cost-effectiveness of screening for gestational diabetes mellitus (GDM) in primary and secondary care settings, compared with a no-screening option, in the Republic of Ireland. Methods The analysis was based on a decision-tree model of alternative screening strategies in primary and secondary care settings. It synthesised data generated from a randomised controlled trial (screening uptake) and from the literature. Costs included those relating to GDM screening and treatment, and the care of adverse outcomes. Effects were assessed in terms of quality-adjusted life years (QALYs). The impact of the parameter uncertainty was assessed in a range of sensitivity analyses. Results Screening in either setting was found to be superior to no screening, i.e. it provided for QALY gains and cost savings. Screening in secondary care was found to be superior to screening in primary care, providing for modest QALY gains of 0.0006 and a saving of €21.43 per screened case. The conclusion held with high certainty across the range of ceiling ratios from zero to €100,000 per QALY and across a plausible range of input parameters. Conclusions/interpretation The results of this study demonstrate that implementation of universal screening is cost-effective. This is an argument in favour of introducing a properly designed and funded national programme of screening for GDM, although affordability remains to be assessed. In the current environment, screening for GDM in secondary care settings appears to be the better solution in consideration of costeffectiveness.