I retrospectively reviewed the records of 111 patients who had pyogenic vertebral osteomyelitis unrelated to an open procedure on the spine. The mean age at the time of the diagnosis was sixty years (range, eighteen to eighty-four years); sixty-one patients (55 per cent) were sixty years old or more. Forty-four patients (40 per cent) had an impaired immune system secondary to diabetes mellitus, the use of corticosteroids, chemotherapy for cancer, rheumatic or immunological disease, renal or hepatic failure, malnutrition, or myelodysplasia. Magnetic resonance imaging, critical for the determination of an early diagnosis, was performed for 103 patients (93 per cent). The infection in sixty-eight patients (61 per cent) was diagnosed within one month after the onset of symptoms. The most frequent infecting organism was Staphylococcus aureus (forty patients; 36 per cent). The infection in forty-one patients (37 per cent) was caused by organisms, such as Staphylococcus epidermidis, Propionibacterium acnes, and diphtheroid species, that are traditionally considered to be of low virulence. The urinary tract was the most frequent source of infection (confirmed in thirteen patients and suspected in twenty-one). The success of non-operative treatment was predicted by four independent variables: an age of less than sixty years, the immune status, infection with Staphylococcus aureus, and a decreasing erythrocyte sedimentation rate. Forty-two patients were managed with debridement and arthrodesis. Fourteen of these patients also had instrumentation of the spine, in the presence of infection, without compromise of the outcome. Eighteen patients died by the time of the latest follow-up evaluation at a mean of four years (range, two years and two months to six years and six months): seven who had been managed non-operatively died in the first month after the diagnosis was made, three died in the acute postoperative period, three died of late complications of paraplegia, and five died of unrelated causes. None of the eighty-nine patients who were seen at a minimum of two years postoperatively had had late recurrence of infection. Chronic, severe back pain was noted in only seven patients.