Litter sizes (LS) for the three largest breeds of sheep represented in the Swedish sheep recording scheme, Pelt (P), Swedish Crossbred (X) and Landrace Finewool (F), were studied. Average LS for different ewe ages were seen to increase from yearling to full maturity, around 4 years of age, and then remained the same until around 9 years of age for P and X, which thereafter showed a slight decrease. Landrace Finewool, a more prolific breed, peaked at 5 and 6 years of age and started to decline the year after. Flock size in itself did not significantly affect LS for any breed. The addition of an effect of flock-year increased the coefficient of determination (R2) in a linear model. SAS Proc CATMOD estimated noticeable differences between LS distributions for different breeds and ewe ages, and smaller differences between LS distributions for individual ewe deviations from flock average lambing date. It was concluded that the effects of flock-year and age of ewe were the major fixed effects that need to be accounted for when evaluating LS within breed.