Medical devices associated infections continue to be a significant source of morbidity and mortality in patients requiring devices and increase medical expenses by prolonging hospitalization. These infections are most commonly caused by biofilm producing organisms. Objectives: to study microbial biofilms in different medical devices, bacteriologically and morphologically, and their association with diseases and antimicrobial resistance. Methods: 103 patients with different indwelling medical devices were studied to isolate and identify the organism present on the device surfaces and to test for biofilm production using tube and plate adherence methods as well as spectrophotometric methods. Also, the organisms were studied for antimicrobial resistance using Calgary’s devices. Scanning Electron microscopy was used on some of the devices to confirm the presence of the biofilm. Results: The results revealed isolation of different species from 65.1% of the studied devices. Associated infections detected by blood and urine cultures were 48 % and 61% respectively. Biofilm production by the isolates showed that 11.9% were weak, 17.9% were strong, and 70.2% were non producers. Staphylococcus spp. represented 40% of organisms producing biofilm. Antimicrobial resistance showed statistical significant difference between planktonic and biofilm cells as measured by MIC and MBEC (p< 0.001). In conclusion: This study indicated that there were a significant percentage of organisms able to grow within biofilm produced on indwelling medical device surfaces and considered as a source of infections. Plate adherence and spectrophotometric methods both are reliable tests, by which we can use any of them to diagnose biofilm formation. The choice depends on the availability of different reagents and equipment. Spectrophotometric method is the most reliable test to differentiate between weak and strong biofilm producers compared with the tube method. Biofilm producing isolates were highly resistant to the antimicrobials in comparison to their planktonic counterparts.