Introduction Quality and safety of laboratory diagnostics have very important and significant affect on the promotion of a overall health care. Classification of laboratory diagnostics to the preanalytical, analytical and postanalytical phase, facilitates the monitoring of the entire laboratory process, as well as the emergence of possible errors. A lot of evidence are suggesting that the preanalytical phase is the most critical part of this given process. Some problems which occur in the given phase include non-compliant samples due to the misidentification, quantity (insufficient sample volume for analysis) or quality (hemolysed, clotted, contaminated samples) of the samples. Standardization of the entire process and the timely detection of errors leads to higher quality of laboratory diagnostics. In the microbiological diagnostics, one needs to know the principles and details of taking and sending samples to the microbiology laboratory, since it is particularly important to preserve in sample as many of those present infectious particles. Objective The objective of this paper is to present and point out most common errors occuring in the preanalytical and analytical phase of work in the microbiology lab in order to avoid them. Sources of information and methods Each lab requires a detailed knowledge of principles, which good laboratory practice has; ie. to comply with the standard criteria of protection at work. The most important and the simplest way to prevent and control infections is a hand hygiene. As the replacement samples for most common causes of errors, it is important to correctly and completely fill microbiological referral since it is sometimes the only valuable communication between the laboratory and the clinic. For samples, it is most important to choose a good, properly taken and quickly transported to the microbiology lab. To be valid, samples must represent an infectious process. Microbiology processes almost all clinical specimens, primarily sterile and non-sterile, for the requested infections (bacterial, viral and fungal) under the relevant rules of sampling, storage and transport; as well as the any deviations leading to a non insignificant preanalytical errors. In the analytical part of the process it is important to correct processing of the samples to the appropriate methods, direct and indirect. Conclusion Most errors in laboratory work are carried out in preanalytical stage. The aim of all laboratories is to improve the general quality and accuracy of the findings, and this can be achieved only through a detailed and continuous staff training. In microbiological diagnostics, one has to work on the quality of samples which will affect the reduction of the preanalytical and analytical errors.