CRISPR/Cas9-based gene targeting allows deletion of a gene of interest from cultured cell lines. Due to difficulty in transiently transfecting hematopoetic cells with components required for this process, we have adopted a lentiviral system for delivery of the CRISPR/Cas9 components into myeloid cell lines. Here, we detail the process of knocking out genes from pools of cultured myeloid cells using this CRISPR/Cas9 system and describe methods of validating these knockout pools.