Back ground:chronic osteomyelitis is severe, persistent and sometimes incapacitating infection of bone and bone marrow. Malnutrition and infection exacerbate one another in vicious cycle. Chronic osteomyelitis specifically affects nutritional status by increasing protein and energy requirement. Evidence shows that nutritional status or malnutrition remains undiagnosed in up to 70% of hospital patients. Objective: To assess nutritional status and associated factors among adult chronic osteomyelitis patients in Felegehiwot Referral Hospital from April 17-May 17, 2017. Method: Institution based cross sectional study was conducted in Felegehiwot referral hospital bu ising systematic random sampling technique. The data was collect by using clinical assessment, measurements and interviewer administered semi-structured questionnaire. Both Bi variate and Multivariate logistic regressions were used to by using spss and epi info soft wares. Result: A total of 241 chronic osteomyelitis patients were included in the study and 238 responded which make the response rate 98.7%. The Mean (+standard deviation.) age of the respondents was 29(+11.8) years. Prevalence of malnutrition was 56.4% 95% CI (47.8%60.5%).Monthly income[AOR= 0.093; 95% CI (0.009, 0.955)]92.7%protective food intake [AOR= 3.080;95%CI(1.485,6.387)]and dietary counseling[AOR=3.526; 95% CI(1.424,8.73)] were significantly associated with malnutrition . Conclusion: There is a high burden of malnutrition in adult chronic osteomyelitis patients.loss of appetite, food intake, house holdmonthly income and dietary counseling were associated with malnutrition in these patients.Treatment of chronic osteomyelitis should be accompanied by nutritional support . Recommendations: Targeted interventions such as nutritional status assessment and management, dietary counseling should be the key intercession during the course of chronic osteomyelitis treatment and follow up.