Precision of ages was estimated in three replicates among six readers from scale samples of rainbow trout Oncorhynchus mykiss of two different life history types, lacustrine and riverine. Logistic regression was used to examine the affect of experience level on the probability of repeating estimates among replicates. Analysis of variance models were used to examine the difference in mean modal age estimates among readers. Experience was found to be related to the probability of repeating estimates among replicates for riverine rainbow trout, but not for lacustrine rainbow trout. Mean modal ages varied significantly among readers, but the variation was not found to be related to experience. A procedure for reading rainbow trout scales is proposed which attempts to minimize both between and within-reader aging variability.