SIBMED ((SIBpair Mutation and Error Detection)) is a FORTRAN 77 program that identifies likely genotyping errors and mutations for a sib pair in the context of multipoint mapping.Specifically, using a hidden Markov model, the program calculates the posterior probability of genotyping error or mutation for each sib-pair-marker combination, given all the available marker data, an assumed genotype-error rate, and a known genetic map. The subset of combinations for which this posterior error probability is high may be considered for exclusion, review, or retyping.