Oligosaccharides are the third largest solid component in human milk. These diverse compounds are thought to have numerous beneficial functions in infants, including protection against infectious diseases. The structures of more than 100 oligosaccharides in human milk have been elucidated so far.The aim of this review was to identify the main factors that affect the concentrations of oligosaccharides in human milk and to determine whether it is possible to calculate representative and reliable mean concentrations.A comprehensive literature search on oligosaccharide concentrations in human milk was performed in 6 electronic databases: BIOSIS, Current Contents Search, Embase, Lancet Titles, MEDLINE and PubMed.The initial search resulted in 1363 hits. After the elimination of duplicates, the literature was screened. The application of strict inclusion criteria resulted in 21 articles selected.Oligosaccharide concentrations, both mean values and single values, reported in the literature were sorted by gestational age, secretor status of mothers, and defined lactation periods.Mean concentrations, including confidence limits, of 33 neutral and acidic oligosaccharides reported could be calculated. Concentrations of oligosaccharides in human milk show variations that are dependent on both the secretor type of the mother and the lactation period as examined by analyses of variance. In addition, large interlaboratory variations in the data were observed.Worldwide interlaboratory quantitative analyses of identical milk samples would be required to identify the most reliable methods of determining concentrations of oligosaccharides in human milk. The data presented here contribute to the current knowledge about the composition and quantities of oligosaccharides in human milk and may foster greater understanding of the biological functions of these compounds.