It is known that Fe deficiency has a negative impact on cognitive function in children by altering brain energy metabolism and neurotransmitter function. It is unclear whether Fe deficiency has detrimental effects on cognition, mental health and fatigue in women of childbearing age. Our aim was to systematically review the literature to determine whether Fe deficiency in women of childbearing age affects cognition, mental health and fatigue, and whether a change in Fe status results in improvements in cognition, mental health and fatigue. Studies using Fe supplement interventions were reviewed to examine the effect of Fe deficiency in women of childbearing age (13–45 years) on their cognition, mental health and fatigue. English-language articles ranging from the earliest record to the year 2011 were sourced. The quality of retrieved articles was assessed and the Fe pathology, cognitive, mental health and fatigue data were extracted. Means and standard deviations from cognitive test data were included in meta-analyses of combined effects. Of the 1348 studies identified, ten were included in the review. Three studies showed poorer cognition and mental health scores and increased fatigue with Fe deficiency at baseline. Seven studies reported an improvement in cognitive test scores after Fe treatment. Results of three of these studies were included in meta-analyses of the effect of Fe supplement intervention on cognition. The results of the meta-analyses showed a significant improvement in Arithmetic scores after treatment (P < 0·01), but no effect on Digit Symbol, Digit Span or Block Design. While an improvement in cognition after Fe treatment was seen in seven out of ten studies, the evidence base is limited by poor study quality and heterogeneity across studies. Additional high-quality studies using consistent measures are warranted.