Summary Eight years of records for 1495 beef heifers from two Kansas herds were analyzed to determine some of the causes of dystocia in primiparous heifers and its effects on subsequent reproductive performance and weaning weights of progeny. Records from spring calving Simmental (SS); fall calving Simmental (SF) and fall calving Angus (AF) heifers were analyzed. Percentages of heifers requiring assistance at first parturition for the SS, SF and AF were 57%, 38% and 36%, respectively. Calves requiring assistance produced heavier (P = .01) birth weight calves with increased (P=.01) ca lf mortality at birth. Conception rates during a subsequent 63 day breeding season followed first parturition were lower for assisted than unassisted dams. Assisted AF heifers were 7.96 days younger (P than unassisted AF heifers at their first parturition. Assisted SS heifers had a 12.58% lower (P .05) first service conception rate and 15.29% fewer (P assisted heifers calved in the first 21 days of the subsequent calving season than unassisted SS heifers. Calves from assisted SF heifers were 8.2 kg heavier (P .05) at weaning than calves from unassisted dams. Simmental heifers requiring assistance at their own birth tended to require more (P assistance at first parturition. Sire of dam had a significant effect on dam's reproductive and growth performance and on dam's progeny's weaning weight. Dystocia in first calf heifers was associated with heavier birth weights, increased calf mortility and reduced rebreeding, but did not reduce weaning weights of first or second calf.