Simultaneous infections with different Legionella spp. have rarely been described in the literature. We now report on seven sporadic cases of legionellosis of which three were simultaneous infections caused by multiple Legionella pneumophila serogroups. Four different legionellae were involved. L. pneumophila serogroup 1, two different types of L. pneumophila serogroup 4, and L. pneumophila serogroup 10 have been identified simultaneously from a lung tissue specimen of one patient. Specimens from two other patients each revealed two different legionellae of serogroups 1 and 4. The existence of different L. pneumophila serogroups in simultaneous infections has not only been documented by identifying the incriminated Legionella spp. by classical methods. In addition, preliminary results of Legionella spp. identification with the novel physical procedure of Fourier transform infrared spectroscopy have been presented to evaluate its possible applicability for routine diagnostic procedures.