Introduction: Bone and joint infections are common in Africa, they present late and or are diagnosed late and are often treated inadequately. These are a major source of disability in all age groups. Osteomyelitis is an acute or chronic inflammatory process of the bone and its structures secondary to infection with pyogenic organisms such as bacteria or fungi. Statement of the problem: In many parts of the developing world, information regarding the etiology and antibiotic sensitivity pattern of bacteria isolated from osteomyelitis are absent. In the absence of clear indication of the causative organisms, the initial choice of antibiotics is empirical. Antibiotics are therefore abused. Objective: The main aim was to study the microbiology of chronic osteomyelitis and its antibiotic sensitivity patterns at KCMC orthopedic unit from August 2009 to June 2010. Study design: Descriptive prospective hospital based study. Study area: Kilimanjaro Christian Medical Centre orthopedic department. Methodology: Questionnaire and data collecting forms were used to capture demographic characteristic of patients and to record laboratory results. Intra-operative bone biopsies were taken from each patient and subjected to standard culture and sensitivity test for gram negative and positive bacteria. Through culture and sensitivity test the causative bacteria were identified and their susceptibility to antibiotics were determined. Results: In this study a total of sixty patients were enrolled. The study showed that chronic osteomyelitis affected more males than females concentrating at their first and second decade of life. The majority of patients had primary education. The income of the families was less than 30 USD per month. Staphylococcus aureus accounted for 53% of the culture isolates followed by mixed organisms in 16% and Proteus species 10% of cases. Twenty four percent and 53% of isolated staphylococci were resistant to cloxacillin and erythromycin respectively. More than sixty percent of patients had used self prescribed antibiotics. Seventy nine percent of staphylococci were sensitive to ampicillin while 85% were sensitive to gentamycin Conclusion: Staphylococcus aureus remained to be the main culprit in causing chronic osteomyelitis and its susceptibility to antibiotics has changed. In the previous studies done in Tanzania more than 90% of isolated Staphylococcus were sensitive to prescribed antibiotics. Staphylococci, Coliforms and Proteus species were highly susceptible to amikacin and the third generation cephalosporins. These drugs are however very expensive and not widely available Staphylococci in chronic osteomyelitis at KCMC seem to be more susceptible to ampicillin than cloxacillin. Gentamycin remains highly active against staphylococci. Recommendations: A larger study is needed to elucidate further these initial findings.