BACKGROUND In February 2009 an outbreak of subcutaneous abscesses due to Mycobacterium abscessus was detected in Spain which affected healthy women who had undergone mesotherapy procedures in an aesthetic clinic. METHODS Epidemiological research, health inspection and microbiological studies were conducted. The patients were given antibiotic treatment (according to susceptibility testing) with clarithromycin, and in some cases, combined with amikacin. RESULTS Seventeen out of 77 patients treated in the clinic were affected. The products used for the injections were homeopathic drugs in multi-dose vials. The environmental samples were negative. The sterile injection equipment and the clinical procedures were evaluated as correct. The storage conditions for the drugs were also correct, and all the samples tested negative for Mycobacteria. However Paenibacillus provencensis was isolated from samples of unused multi-dose vials and the withdrawal of the product from distribution was ordered. Deficiencies were detected in the sterile products process of at the homeopathic drug factory, so the production line was suspended. CONCLUSIONS The results of environmental investigation suggest the most likely cause of the outbreak could have been the contamination of the products in the factory, although there was no laboratory confirmation. The widespread use of homeopathic products in invasive procedures requires extreme control during the manufacturing, handling and packaging process. It is important to consider mesotherapy and parenteral use of homeopathic medicines as potential sources of infection and therefore the same precautions in the procedures and quality assurance of products should be applied as with any other drug or medical activity.