The aim of this study was to evaluate the influence of lactation length (LL) on the subsequent litter size (LS) in pluriparous and primiparous sows Eighteen commercial hog farms were analyzed over a seven-year period (1996-2003). Feed of the lactating animals was based on commercial ration and water ad libitum, with 79.729 parities grouped into five LL: 8 to 13, 14 to 15, 16 to 17, 18 to 21 and 22 to 25 days. Increased litter size of the subsequent parity (P<0.05) was observed as the lactation period was extended in the pluriparous sows, with 10.70 ± 0.5; 11.16 ± 0.2; 11.15 ± 0.2; 11.34 ± 0.1; 11.87 ± 0.3 for the periods of 8 to 13, 14 to 15, 16 to 17, 18 to 21 and 22 to 25 days, respectively. However, periods of 14 to 15 and 16 to 17 did not show any difference (P>0.05). The primiparous sows produced smaller litter size over the periods of 8 to 13 (10.34 ± 0.9), 14 to 15 (10.41 ± 0.5) and 16 to 17 (10.46 ± 0.6) days, compared to LLs of 18 to 21 (10.68 ± 0.5) and 22 to 25 (11.43 ± 0.8) days. Both the multiparous and primiparous sows had LL from 22 to 25 days, resulting in higher LS (P<0.05), when compared to other LL. It can be concluded that the lactation period has an effect on litter size, with the 22 to 25 length providing better results in the litter size of subsequent parity of the female swine.