Buruli ulcer (Mycobacterium ulcerans) is an emerging disease. The mode of transmission is still unknown. Mycobacterium ulcerans has been detected (by polymerase chain reaction) in water and water insects. Extensive surgery is still the main treatment. Recognition and excision - of the early nodular stage - is effective. The toxin, a polyketide, causes immunosuppression with potent inhibition of monocytes, T cells and nuclear factor kappa-B activation.