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The objective of this work was to evaluate the effects of sex of lamb (SL: male, female), type of birth (TB: single, twin), age of dam (AD: 2 to 7 years and older), farm (F: 10 units), and sire nested within farm, as well as first-order interactions that influence the variation of birth weight (BW), adjusted weaning weight (AWW) and average preweaning daily weight gain (ADG) of Hampshire lambs from 10 farms in Hidalgo, México. A data base from 2006 to 2009 with 998 observations for BW and 933 for AWW and ADG was analyzed. Feeding of parents and lambs was based on grains, alfalfa, oats hay, and minerals. The statistical analysis was carried out with the GLM procedure of SAS. Overall means were BW: 5.1±0.9 kg, AWW: 32.3±5.4 kg, and ADG: 0.300±0.055 kg. Significant effects (P<0.01) due to sex of lamb were observed in the three variables analyzed, males had the highest averages; type of birth (P<0.01) only on BW and AWW, the highest averages were obtained by lambs of single birth; age of dam on BW (P<0.01) and AWW and ADG (P<0.05), lambs born to dams from 3 to 5 and 7 years and older had the highest averages in the three variables. Sire nested within farm had a significant effect (P<0.01) on AWW and ADG. It is concluded that there are important environmental factors influencing pre-weaning traits of Hampshire lambs, useful information that must be considered for management purposes and genetic improvement in these farms. [ABSTRACT FROM AUTHOR]