Antimicrobials are considered as the greatest discovery of twentieth century. But irresponsible and erratic use of these life-saving instruments has resulted in development of drug-resistance in many organisms and many side effects. The aim of this work was to study the side effects of antibiotic abuse and to correlate the side effects with the benefits and efficacy. The study was done in Abou El Rish university hospital cairo university and included 90 patients who were divided into three age groups. Investigation were done before and after the use of antibiotics namely (CBC-liver and kidney functions-Blood and urine cultures- CRP).The results showed significant diarrhea ,neutropenia and increase in renal functions with use of amoxicillin ,carbapenem and vancomycin in order.