Ribotyping, a method of strain identification based on analysis of bacterial genomic restriction fragment length polymorphisms, was used to investigate the acquisition of Pseudomonas cepacia by a patient with cystic fibrosis. Analysis of isolates recovered from the index patient and his contacts showed person-to-person transmission of this opportunist organism. This documentation of the transmission of P cepacia from one cystic fibrosis patient to another suggests that measures to limit the acquisition of the pathogen by patients with cystic fibrosis may be worth while.