It is well established that in mammals transitory zinc (Zn) deficiency during embryogenesis can have a negative influence on fetal development. Similar to Zn deficiency, maternal exposure to low levels of ionizing radiation during the first day of pregnancy has been shown to negatively affect preimplantation embryo development, and higher doses of maternal irradiation during late stages of embryogenesis can result in malformations. Here we report the effect of transitory maternal Zn deprivation combined with low dose irradiation during embryogenesis on fetal outcome. Pregnant mice were acutely dosed with 0.00, 0.05, 0.10, or 0.25 Gy of gamma-radiation the day after mating (GD0), or with 0.00 or 0.50 Gy on GD8. Mice irradiated on GD0 were either fed a low Zn diet (0.4 microgram Zn/g) for 48 h prior to mating through GD0 or GD5 and then switched to a control diet (50 micrograms Zn/g) through GD18, or they were fed the control diet throughout gestation. Dams irradiated on GD8 were either fed the low Zn diet from GD0 through GD10 and then switched to the control diet, or they were fed the control diet throughout gestation. Zn deprivation did not influence any of the maternal or embryonic/fetal parameters measured in the cohorts fed the low Zn diet through GD0. In contrast, groups fed the low Zn diet through GD5 or GD10 had lower mean maternal body weights, fewer live fetuses/litter, and a higher incidence of resorptions than controls. Fetuses from dams fed the low Zn diet through GD10 were smaller and shorter, and had a higher frequency of malformations than controls. Irradiation on GD8 under adequate Zn conditions had no effect on any parameter, but GD8 irradiation during maternal Zn deficiency had an additive effect on the frequency of fetal malformations.