Introduction: Conventional Cytogenetics is an essential tool for the diagnosis of a neoplastic or premalignant condition and provides important prognostic and therapeutic information. The rate of unsuccessful karyotyping in hematological malignancies is reported between 10-20%. Objective: To analyze the relationship between pre-analytical variables and associated failures with conventional karyotyping in hematological neoplasms. Material and Methods: 1020 samples with suspected hematological malignancies received in the department of Cytogenetics from January 2018 to December 2019 were included in the study. Pre-analytical variables assessed included time from collection to sample processing, type of sample, diagnosis and sample cellularity. Statistical analysis was performed using Chi-square test to verify associations of variables with karyotyping. Results: 86 (12%) out of 720 samples that were processed in less than 24 hours of time of collection showed an unsuccessful KT while 57/300 samples (19%) that were processed beyond 24 hours failed to yield any metaphase (p-value 0.003). 31/79 PVB (39%) and 112/941 BM (12%) were unsuccessful (p-value __ampersandsignlt;0.001). 15/287 (06%) acute myeloid leukemia cases, 64/156 (41%) acute lymphoblastic leukemia cases, 12/109 (11%) myelodysplastic syndrome, 6/34 (18%) MDS/MPN cases, 11/338 (03%) MPN cases and 35/96 (36%) from the others category did not yield any metaphase for analysis (p value 0.015. 24/819 (03%) samples with cellularity __ampersandsigngt;7 x 103/__ampersandsignmu;l and 119/201 (59%) samples with low cellularity being __ampersandsignle;7 x 103/__ampersandsignmu;l were unsuccessful (p-value __ampersandsignlt;.001). Discussion: Rate of unsuccessful karyotyping was 14% that was significantly associated with the time to process, nature of sample and cellularity. Conclusion: Collection of an adequate and good quality sample is of paramount importance on which success of karyotyping of hematological malignancies depends.