A six-month prospective study was conducted in Holeta, Debre Zeit and Muke Turi dairy fannsrnbetween November, 2007 and April, 200S with the major objective of determining both therncumulative incidences of neonatal calf diarrhoea (NCD) and pneumonia. In addition,rndetermination of calf mortality rates, identification of agents of NCD, pneumonia and potentialrnrisk factors as well as determinations of the antibiotic sensitivity patterns of the bacterialrnpathogens.rnCluster sampling was used. A total of 429 calves, from seven intensive dairy farms werernfollowed up. The farms were described using a pre-tested questionnaire and personalrnobservations. Study calves in each fann were visited weekly and appropriate test samplesrncollected from diarrhoeic and pneumonic cases.rnAntigenic ELISA test was utilized to identify four major enteropathogens (rotavirus, coronavirus,rnCryptosporidium parvum and E. coli K 99). Standard isolation techniques were used to identifyrnSalmonella and other strains of E. coli from diarrhoiec cases (n=112) and Pasteurella species,rnMannhaemia species and Haemophilus somnus from pneumonic cases (n=2S). In addition, thernantimicrobial susceptibility pattern of the bacterial isolates was performed.rnThe cumulative incidences (CI) of NCD in Holeta, Muke Turi and Debre Zeit dairy farms werern0.41, 0.63 and 0.37, respectively. While for pneumonia, they were 0.12, 0.09 and 0.07,rnrespectively. Higher CI ofNCD was recorded from Farm 1 with 0.65 followed by Farm 3 withrn0.63. The least CI was observed in Fann 2 of 0.11. Highest calf pneumonia was observed inrnFarm 6 followed by Farm 1. No calf pneumonia was observed in Farm 5.rnAssociations of the potential risk factors for NCD and pneumonia revealed significant resultsrnwith young ages. Significant positive hazard rates of both diseases were recorded in young agegroups.rnOther risk factors (.sex of calves, breed, etc) were not significantly associated with theserndiseases.rnThe ELISA results showed that, C. parvum was prevalent in the majority of calves with diarrhoearnfollowed by rotavirus, coronavirus and E. coli K 99. The bacterial isolates were 91.96 % of E.rnIXrncoli other than the strain K 99 and 24.11 % of Salmonella species. Nasal swab samples taken forrnisolation of Pasteurella and Mannhaemia species revealed 42.85 % positive reactors forrnPasteurella and Mannhaemia species. No Haemophilus somnus was isolated.rnAntimicrobial sensitivity test was perfonned for all the bacterial isolates. Norfloxacillin andrngentamycin were highly sensitive and clindamycin the least sensitive. The susceptibility to otherrnantimicrobial agents varied by different bacterial isolates, but resistance to all antimicrobials usedrnwere observed in most of the isolates.rnIn conclusion, NCD is a serious problem among dairy calves followed by pneumonia. Both ofrnthem were influenced by the age of calves. These diseases have complex etiopathogenesis.rnTherefore, further epidemiological and microbiological studies ofNCD and pneumonia with aimsrnof designing and implementing appropriate prevention and control strategies are stronglyrnrecommended. In addition, the higher rate of antimicrobial resistance necessitates the strategicrnuse of the drugs.rnKey words: Neonatal calf diarrhoea, Calf pneumonia, rotavirus, coronavirus, Cryptosporidiumrnparvum, Escherchia coli, Salmonella, Pasteurella, Mannhaemia, Haemophilus somnus