The reproductive performance (fertility and prolificacy) of Finnish Landrace (Finn) and Suffolk sheep on an accelerated breeding program was evaluated. Both breeds were contained in each of two separate flocks housed indoors year-round on expanded metal floors in windowless buildings. The two flocks were bred alternately at 4-mo intervals in January, May and September. The sheep were exposed to either an abrupt (ALR) or constant (CLR) lighting regimen. Data from nine breedings during a 4-yr period were considered. Fertility was significantly higher for ewes in the ALR lighting regimen. Fertility was lower for ewes bred in September. For ewes that had lambed from breeding 8 mo earlier, fertility was higher for Finn ewes than for Suffolk ewes; however, similar fertility levels were observed in both breeds if the ewes had not lambed following the previous breeding. Higher prolificacy was observed in the Finn ewes than in the Suffolk ewes, but the differences in prolificacy varied with the month of breeding. The probability of a ewe having more than one lamb was significantly higher for Finn ewes than for Suffolk ewes in both January and May breedings, but was similar in September breedings. Incorporating the Finnish Landrace breed into an accelerated breeding program for sheep maintained indoors year-round is a practical way to increase the number of lambs born. Controlling daylength and dividing the flock into smaller flocks are also practical procedures to increase lamb production.