Objectives were to evaluate the association between gestation length (GL) and incidence of diseases, reproduction, and milk production. The data were screened to eliminate cows with GL longer or shorter than 3 SD from the population mean, resulting in 104 cows excluded from the analyses. Holstein cows (n = 6,254) on a farm using only artificial insemination (AI) were evaluated. Responses measured included the incidences of stillbirth, retained placenta (RP), metritis, mastitis, and other diseases within 90 d in milk (DIM). Pregnancy at first AI and interval to pregnancy were evaluated. Milk yield and removal from the herd by death or culling were recorded for the first 300 DIM. Gestation length was categorized as short (S; at least 1 SD below the population mean; group mean = 266, range 256 to 269), normal (N; population mean ± 1 SD; group mean = 276, range 270 to 282 d), and long (L; > 1 SD above the population mean; group mean = 285, range 283 to 296 d). Data were analyzed by ANOVA, logistic regression, and the Cox’s proportional hazard model using the GLIMMIX and PHREG procedures of SAS. Models included the fixed effects of GL category (S, N, L), gender of calf (female, male, twin), parity (1 or >1), season of calving (cool or hot), and all 2-way interactions. Gestation length affected (P < 0.01) the incidences of stillbirth (S = 11.4, n = 7.3, L = 6.7%), RP (S = 32.7, n = 10.3, L = 9.4%), metritis (S = 51.1, n = 36.5, L = 33.9%), but not (P = 0.85) that of mastitis (S = 4.7, n = 4.0, L = 5.2%). The rate of removal from the herd by culling or death was faster (P < 0.01) for S than N (adjusted hazard ratio [HR] = 1.32; 95% CI = 1.10–1.58) and tended (P = 0.10) to be faster for L than N (adjusted HR = 1.12; 95% CI = 0.98–1.29). Pregnancy at first AI did not differ (P = 0.94) among groups (S = 33.2, n = 34.3, L = 33.5%). The rate of pregnancy was greater (P < 0.05) for N than L (adjusted HR = 1.11; 95% CI = 1.02–1.21), but it did not differ between N and S or L and S. Daily milk yield was greater (P < 0.01) for N than S or L (S = 35.2, n = 38.1, L = 35.8 ± 0.4 kg/d). Cows with GL within 1 SD of the population mean (range 270 to 282 d) had improved health, reproduction, and production.