A longitudinal prospective observational study on calf diarrhea and mortality in dairy farms inrnand around Addis Ababa was conducted from October, 2006 to May, 2007 with the objectives ofrndescribing incidence of calf diarrhea and mortality and identification of potential pathogensrnassociated with calf diarrhea. A total of 254 calves; 37 from four large dairy farms and a randomrnsample of 217 calves from market oriented smallholder and medium-sized dairy farms werernincluded in the study. Each calf was individually identified and regularly monitored for clinicalrnhealth problems up to the age of six months. Information on different management aspects wererncollected by personal observation during the regular visit to farms and from questionnaire surveyrnconducted during the study period. Fecal samples were also aseptically collected from diarrheicrncalves for laboratory examination to detect entropathogens involved. Rotavirus, Coronavirus,rnEscherichia coli K99 and Cryptosporidium parvum were detected using antigen ELISA.rnSalmonella were isolated and identified following ISO 6579 (2002) and Quinn et al. (1994).rnAntimicrobial susceptibility test for Salmonella isolates was also done following NCCLS (1997)rnguidelines. The overall incidences of calf diarrhea and crude mortality found in this study werern33.6% and 11.6%, respectively. Other disease conditions that were diagnosed in calves includedrnnavel ill, joint ill, pneumonia, septicemia, congenital loss of vision and other miscellaneous cases.rnThe incidence of calf diarrhea was apparently higher in medium-sized and large dairy farms thanrnsmallholder dairy farms while the incidence of calf mortality was higher in smallholder and largerndairy farms. Based on laboratory examination, Rotavirus, Coronavirus, E. coli K99,rnCryptosporidium parvum and Salmonella were detected from diarrheic calves at rate of 1/36rn(2.8%), 3/36 (8.3%), 8/36 (22.2%), 23/36 (63.9%) and 6/36 (16.7%), respectively. The serotypesrnof Salmonella identified were Salmonella Typhimurium (4/6), S. Dublin (1/6) and S.rnMishmarhaemek (1/6). Of the serotypes tested for resistance to a panel of 13 antimicrobial agentsrnall isolates of Salmonella Typhimurium showed intermediate resistance to one or more drugs.rnSalmonella Dublin was intermediate in resistance to tetracycline, kanamycin and nalidixic acid.rnAll serotypes tested were resistant to erythromycin. In conclusion, the incidence of calf diarrhearnand mortality found in this study were high and could affect dairy production through substantialrneconomic losses mainly due to morbidity, cost of treatment, mortality and future productivity. Allrnpotential pathogens were detected in diarrheic calves. Some of these pathogens such asrnVIIIrnCryptosporidium and Salmonella are zoonotic and hence can serve as source of infection tornhumans. Control and management of calf diarrhea should focus on reducing exposure to therninfectious agents and optimizing the calvesâ€™ resistance to them.