Focal segmental glomerulosclerosis is a nonspecific renal lesion observed both as a primary (idiopathic) entity and in a secondary form, typically in association with reduced functional renal mass. Familial forms have been observed and two loci for autosomal dominant FSGS have been mapped. This study shows that an adolescent/adult form of recessive FSGS maps to a locus on chromosome 1q25-31, which overlaps with a region previously identified as harboring a locus for an early childhood onset recessive form of nephrotic syndrome (SRN1). Evaluation of a large family demonstrated linkage with a maximum two-point lod score of 3.98 at D1S254 and D1S222. Lod score calculations support the conclusion of linkage in four of five additional families. Haplotype analysis suggests that this FSGS gene is located in a 19-cM region flanked by D1S416 and D1S413, of which 6 cM overlaps with SRN1, suggesting that these distinct clinical subsets of kidney disease may be allelic. These regions may also overlap with the syntenic region of the glomerulosclerosis susceptibility locus in the BUF/Mna rat. Because the presentation of FSGS may be subtle, inherited FSGS may be much more common than generally realized and grossly underestimated because of the absence of clear familial patterns. This result increases the suspicion that polymorphisms at this locus may contribute to sporadic FSGS.