BACKGROUND/AIMS: Haemangiomas are common benign tumours of infancy that consist of rapidly proliferating endothelial cells. A locus for an autosomal dominant predisposition to haemangioma has been identified recently on chromosome 5q. This study aimed to investigate loss of heterozygosity on chromosomes 5 and 9 in haemangiomas. METHODS: Sporadic proliferative phase haemangiomas were microdissected. Polymerase chain reaction amplification and analysis of microsatellite markers on chromosomes 5 and 9 was carried out. RESULTS: There was a significant loss of heterozygosity for markers on chromosome 5q in haemangioma tissue, when compared with either markers from chromosome 5p (p < 0.05) or markers from chromosome 9 (p < 0.05). CONCLUSIONS: These results suggest that haemangioma formation might be associated with somatic mutational events, and provides evidence that a locus on 5q is involved in the formation of sporadic haemangiomas.