We reviewed laboratory, clinical, and epidemiologic data on 35 patients from whom organisms belonging to the genus Roseomonas, a pink-pigmented gram-negative coccobacillus, were isolated over a 22-year period (1972-1994). Roseomonas strains were most commonly isolated from middle-aged women with one of several underlying conditions, including cancer and diabetes. Roseomonas was most commonly isolated from the blood, in association with clinical signs of sepsis. Approximately 60% of all isolates were judged to be of possible clinical significance, either as primary or secondary pathogens; 75% of all strains were recovered in pure culture. Roseomonas gilardii was the most frequently isolated species and was significantly associated with septicemia and underlying immunocompromised conditions; the species of 29% of all Roseomonas isolates could not be unequivocally identified with presently available differential tests. Genomospecies 5, currently an unnamed taxon within the genus Roseomonas, was primarily recovered as a commensal from young adults attending a sexually transmitted diseases clinic. The findings suggest that although this genus appears to have an overall low pathogenic potential for humans, Roseomonas species-in particular, R. gilardii-may be significant pathogens in persons with underlying medical complications.