The gene for autosomal recessive proximal spinal muscular atrophy (SMA) has recently been mapped to chromosome 5q12.2-q13, within a genetic distance of about 6 cM, and is proximally flanked by the locus D5S6 and distally by D5S112. Here, we report linkage analyses in 64 SMA families with nine polymorphic markers closely linked to the SMA gene, which allowed us to narrow the SMA region to about 4 cM and to define a new proximal genetic border by the locus D5S125 (EF(TG/AG)n. Based on haplotype analysis and specific recombination events, the following order of the loci was determined: 5cen-D5S76-D5S6-D5S125-SMA-(5'MAP-1B-3'MAP- 1B)/D5S112-JK53CA1/2-(D5S39-D5S127)-5qter. The location of the SMA gene between D5S125 and MAP-1B is further supported by multipoint linkage analysis.