The diagnosis of blast cell presence in cerebrospinal fluid (CSF) in acute leukemias (AL) is made using techniques such as flow cytometry (FCM) and conventional cytology (CC). This study aims to evaluate CSF blast cell presence frequency in LA using both techniques (CC and FCM) in our center. Methods: We analyzed three hundred and eight CSF samples belonging to 175 patients, 57% male, with a median age of 46 years (1-70 years) were analyzed. Diagnoses were acute B lymphoblastic leukemia (B-ALL, 84%), acute T lymphoblastic leukemia (T-ALL 5%), acute myeloblastic leukemia (AML, 11%). The immunophenotype was performed with an 8-color panel adapted to the diagnosis. Results: The proportion of non-assessable CSF samples in LA was higher for CC (46%) than FCM (4%) (p<0.05). Overall, infiltration was found in 78/308 samples by FCM (25.3%) and in 8/77 by CC (10.4%) (p<0.0001). Seventy of 259 samples were positive in B-ALL (27%) and 6/34 in AML (17%). There were no CC+ cases in AML or T-ALL. The samples that were FCM+/CC+ had more significant infiltration (59.5%) than CMF+/CC- ones (30%) (p<0.0001). Conclusions: CMF detects more than twice as many CSF blast-positive cases in LA as CC and is, therefore, suitable for routine use along with CC.