Bacillary angiomatosis (BA) is a recently described infection usually found in patients with human immunodeficiency virus disease. BA is caused by a Gram-negative coccobacillus. This organism is primarily responsible for skin lesions of the pseudo-botryomycoma type or inflammatory nodules, but it also produces fever, degradation of the general condition and visceral lesions involving the lymph nodes, the liver, the spleen and the bones. Histology shows vascular proliferation with turgid endothelial cells and mostly neutrophilic inflammatory infiltrates. BA is susceptible to many antibiotics. The authors describe the history of the disease and its clinical and histological features, discuss its differential diagnosis and principally deal with the relationship between BA and cat-scratch disease and between BA and verruca peruana. They also present the molecular biology technique which enables a genotypic diagnosis of the disease to be made, replacing a deficient phenotype.