Power calculations for linkage analysis are typically conducted on the assumption of a single locus that affects the trait. Here we report a simple procedure for conducting a power analysis for a genome-wide linkage scan of a quantitative trait under the influence of multiple loci. This procedure is designed for sib pair data analysed by the new Haseman–Elston regression method. The results show that samples as large as 10 000 sib pairs will often not allow quantitative trait loci (QTLs) to be clearly identified. Instead, linkage genome scan using sib pairs must be regarded as a blunt screening tool that will help to focus attention to 10%, or more, of the genome.