The study of the nonconformities (NC) literatures in medical biology report that between 60-85% of laboratory errors are produced during the pre-analytical phase, which are often external and escapes the biologist's control. The objective of our study was to identify the factors at the origin of non-conformities during this phase at the University Hospital of Rabat. A mixed analytical descriptive study realized between August 2019 and August 2020 based on a non-compliance form, a self-questionnaire, an observation grid, focus groups and semi-structured interviews. We also set up the Deming wheel PDCA as well as the work tools (BRAINSTORMIN, 5M, ISHIKAWA). Our results show that 22 % of the prescriptions of biologic tests are drafted by nurses and not doctors this in the absence of an updated list of biological exams. The samples are taken at 88,1% by unqualified personnel and 95 % without any guide or manual. For the traceability aspect, the name of the sampler is never placed on the sheet of examination, age, sex of the patient; time and nature of the sample are often not mentioned in the label vials of samples. Transportation is made by pneumatic cylinder system and sometimes by unqualified staff in absence of procedures for packaging and transportation equipment without traceability. The reception of samples is carried out by untrained staff on the error management of the pre-analytical phase. They result at first from a major defect of coordination between the laboratory and the services, then by the lack of continuing education and the weak competence of the staff involved in this process and finally compounded by the lack of manual sampling, procedures for packaging, transport, reception and triage.