The Spanish haematology external quality assessment scheme (EQAS), established in 1984, is run by the Spanish Haematology and Haemotherapy Association (AEHH) [Quality Assurance in Health Care 3 (1991) 75] and functions to evaluate the quality and reproducibility of the assessment of diagnostic samples by clinical laboratories. The Hospital Clinic of the University of Barcelona (HCB) serves as the EQAS Coordination Centre and follows the guidelines established by the International Committee for Standardization in Haematology [Annali dell'Istituto superiore di Sanità 31 (1995) 95; International Journal of Hematology 68 (1998) 45]. During the period 2001-2006, replicates of 25 different blood films were sent to 604 EQAS participants for cell morphology evaluation. Some patient details corresponding to the samples were disclosed, such us age, sex, haemoglobin value and white blood cell count. The participants were asked to select up to four significant morphology features using a coding list, provided by the Coordination Centre, which included significant morphological alterations that appear in haematopoietic cells. For each survey, individual results were assessed against the morphological reference results (MRR) established by the Cytology Group of the AEHH ('true' answers). This paper describes the organization of the 6-year-long study and the evaluation of laboratory performance for blood smear interpretation by the Spanish haematology EQAS. Different performance levels were detected relative to the laboratory category. Laboratories providing services to hospitalized patients showed higher performances compared with laboratories providing services to nonhospitalized patients. Pathological lymphoid cells were the most difficult to identify by the participants. To improve the results in EQAS peripheral blood morphology, the development of specific cytology educational trainings is discussed.