A review of the literature on sleeping "disorders" in infants and toddlers shows that sleep problems are very common. We report the results of a German multicenter epidemiological study on a birth cohort (N = 1314). The children had medical examinations at 4 weeks, 3 months, 6 months, 1 year, 18 months, 2 years and 3 years. Most of the information on the sleeping behavior was gathered by structured interview and questionnaires. This paper gives information on the prevalence and the persistence of sleep problems in one to three year old children in Germany. Statistical analysis of correlations between breastfeeding and sleep and the place of sleep are reported. The consequences of sleep problems on the family overall well-being are also examined.