Alport syndrome (AS) is a severe hereditary disease usually transmitted as an X dominant trait and involving a mutation of the COL4A5 (type IV collagen, alfa-5 chain) gene. COL4A3 gene (type IV collagen, alfa-3 chain), or COL4A4 gene (type IV collagen, alfa-4 chain) or COL4A5 gene (type IV collagen, alfa-5 chain) genes. Mutations in either the COL4A3 gene or the COL4A4 genes, encoding the 3 and 4 chains of type IV collagen, are responsible for the autosomal-recessive form of Alport syndrome as well as benign familial hematuria (BFH). In a large Multicentre study including more than 300 patients and family members from Slovenia, France, Macedonia, Poland, Australia, United States and Turkey with some clinical symptoms for ei ther AS or BFH screening of COL4A3, COL4A4 and COL4A5 genes was provided. For each patient 150 exons with boundary intronic sequences were first analyzed with polymerase chain reaction (PCR) based single stranded conformational analysis (SSCA) and than samples showing abnormal mobility shift were sequenced. Twenty five novel mutations, six previously described mutations and eleven novel variation and polymorphism were identified. We demonstrated that mutation in either gene COL4A3, COL4A4 or COL4A5, when symptomatic, can be associated with a broad range of phenotypes, from familial benign hematuria to the complete features of Alport syndrome nephropathy. Furthermore our study shows the importance of characterizing the mutation at the molecular level in genetic studies, to understand the relationship between genotype and phenotype.