It has been hypothesised that infancy may be a particularly sensitive period with respect to the effect of dietary sodium (salt) intake on later blood pressure. If this is the case, interventions to reduce dietary sodium intake in infancy could have major public health impact by reducing cardiovascular disease in the future. However, research in this area is hampered by difficulties of how to measure dietary sodium intake in infancy. Here we review the literature with an aim to describe different methods that have been used for research purposes, how these have been used and their relative strengths and limitations. We identified five studies that were relevant to our aim. In epidemiological and intervention studies sodium intake in infancy has been assessed via parents using diet diaries, which appear to be feasible and acceptable to parents. In these studies, sodium concentration in breast milk is assumed not to vary from one woman to the next, which may not be correct but has been poorly studied. The gold standard method - 24 h urinary excretion of sodium - was used in only one study and there is debate about the most appropriate way to collect urine for research purposes in infants. None of the studies directly compared different methods for determining infant dietary sodium intake. We conclude that research is required to determine the best methods of estimating dietary sodium intake in infants in different research contexts.