Members of an international consortium for linkage analysis of the facioscapulohumeral muscular dystrophy (FSHD) gene have pooled data for joint analyses, in an attempt to determine the precise location of the FSHD gene and the order of four DNA markers on 4q35 region. Six laboratories determined a total of 3,078 genotypes in 65 families, consisting of a total of 504 affected subjects and 559 unaffected subjects. For each marker, a mean of 648 meioses were informative. D4S139 and D4S163 were identified as the closest linked markers to the FSHD locus, with 99% upper confidence intervals of recombination fractions of .08 and .10, respectively. We have used the CRI-MAP program to construct the most likely order of cen-D4S171-F11-D4S163-D4S139-FSHD-tel, with favorable odds of 10(8)-10(114) over all other orders except that in which F11 and D4S171 are reversed, for which the odds ratio was 191:1. With this order, the genetic map of this region extends 25.5 cM in males and 13.8 cM in females (averaging 19.5 cM for sexes combined); the sex difference was statistically significant (P = .0013). Comparison between families for the two-point and multipoint lod scores involving FSHD showed no evidence for heterogeneity of this disorder. However, after the completion of this analysis, one large family which might show heterogeneity was identified. In view of this and the fact that all of the linked markers reside on the same side of the FSHD locus, the clinical application of these markers is not recommended at this time.