Our objectives were to evaluate the use of refractometry as a means of estimating immunoglobulin (IgG) concentration of bovine maternal colostrum (MC). Samples of MC (n = 827) were collected from 67 farms in 12 states. Colostrum was analyzed for IgG by radial immunodiffusion (RID) and refractive index (nD) by a digital refractometer. The relationship between nD and IgG was strong (r = 0.73; P < 0.05; n = 823). Samples analyzed by refractometry fresh and went through 1 freeze/thaw cycle prior to RID analysis resulted in the strongest relationship between IgG and nD (r = 0.93 and 0.90, respectively). The MC samples collected fresh (not refrigerated or frozen) on the farm but frozen two or more times prior to analysis by refractometry and RID had a weak relationship between IgG and nD (r = 0.01). Breed and lactation number did not impact the relationship between RID and nD. These results indicate refractometry is an accurate and rapid method to determine IgG concentration when colostrum is analyzed fresh.