Gaucher disease is the most prevalent sphingolipid storage disorder in humans caused by a recessively inherited deficiency of the enzyme glucocerebrosidase. More than 100 mutations have been described in the glucocerebrosidase gene causing Gaucher disease. Some of them are complex alleles with several mutations due to recombination events between the gene and its highly homologous pseudogene. The generation of these recombinant alleles involves, in most cases, a crossover in the 3' end of the gene, beyond exon 8. However, in a few cases recombination took place in a more upstream location. Here we describe the analysis of a patient with type I Gaucher disease who bears a new complex allele. This allele was originated by a crossover between the gene and the pseudogene at intron 2, the most upstream recombination site described so far, which gave rise to a fusion gene. The patient was first diagnosed as homozygous for the c.1226 A --> G (N370S) mutation but the early onset of the disease prompted us to perform parental DNA analysis which showed that the mother was not a N370S carrier, suggesting deletion of at least part of the gene. Molecular analysis of the complex allele was carried out by Southern blot, PCR, and sequencing. We were able to close down the region of the recombination event to an interval of 18 nucleotides, corresponding to the last 15 nucleotides of intron 2 and the first 3 nucleotides of exon 3 of the gene. These 18 nucleotides are identical between the gene and pseudogene making any further refinement impossible. An exhaustive list of published glucocerebrosidase complex alleles, describing their recombination points, is included for comparison.