During the past few years, new information on the pathogenesis of skeletal and joint infections and the host-parasite interaction has been presented. Although this is basic research, several recent case reports have shown that experimental laboratory findings are often relevant for the practical treatment of patients. Bacteria long known as causative agents in orthopedic infections, as well as new and rare ones, challenge our skills in diagnosis and encourage new thinking in host-parasite interaction and epidemiology. Another expanding problem is increased resistance against antibiotics, which is now being observed in pneumococci causing joint infections.