Pre-analytical phase is the most common source of errors in current laboratory practice. With the advent of technology that can implement high quality standards, the frequency of analytical errors has decreased. The aim of our study was to find out the prevalence of preanalytical errors relating to the request forms and sample quality in the clinical biochemistry laboratory of a Medical College Hospital. 4602 samples and their accompanying request forms from the in-patient and out-patient departments were included in the study. Request forms and samples were scrutinized for errors and the results were analysed. The overall prevalence of preanalytical errors was 55.7%, out of which 54.6% was related to request forms and 1.1% was related to specimen collection. Missing clinical diagnosis was the most common error(54.49%)related to request forms. Incomplete filling of request forms appears to be the most prevalent form of preanalytical errors, which can be attributed to lack of awareness among the health care professionals. This being easily preventable, there is an urgent need to sensitize the health professionals regarding the importance of properly filling the request forms.