Objective of the present study was to determine calving parameters in eighteen large dairy herds of Holstein Friesian in Tabriz. Data analysis showed that the mean gestations length were 276.69 ± 6.29, 279.54 ± 8.55 and 271.38 ± 7.34 days in multipara cows and twining pregnancy respectively. Percent of premature birth were 24.14% in twining (28 cases out of in 116 births), 9.61% in heifers (114 cases out of 1186 births) and 4.99% in multipara cattle (132 cases out of 2645 births). Percent of delayed birth were 2.12% in multipara cattle (56 cases from 2645 births). However, there was no case of delayed birth in heifers (out of 1186 cases) and twining parturitions (out of 116 cases). The rate of male progeny was 47.81% (2621 out of 5482 births). The rate of twining birth was 4.06% (211 cases out of 5191 births). The rate of stillbirths was 3.71% (133 cases out of 3589 births) and the rate of dystocia was 4.84% (227 cases out of 4687 births). The rate of posterior presentation was 3.81% (121 cases out of 3178 births) and the rate of retained placenta was 9.15% (335 cases out of 3663 births).This study showed that the gestation length in heifers and twining gestation were lower than those reported gestation length in references.Moreover, the rate of male progeny was lower than the standard ones (p<0.005).