The robust sib‐pair method introduced by Haseman & Elston (1972) is one of the most widely circulated allele‐sharing methods for linkage analysis. The procedure evaluates linkage by significance testing of a regression coefficient and, hence, a standard t‐test has traditionally been applied despite known violations of the statistical assumptions underlying the test. We present a permutation based reference distribution for the estimate of the regression coefficient that is motivated by genetic principles rather than by standard regression testing procedures. The permutation test approximates Mendelian co‐segregation under the null hypothesis of no linkage, making it a very natural approach. Theory and simulations show that the conventional t‐test approximates the permutation test quite well, even when dependent sib pairs are used for analysis. These results thus indirectly address concerns over the t‐test. To illustrate the permutation test using real data we applied the procedure to two lipoprotein systems that have been well characterized.