Patients with chronic lymphocytic leukemia (CLL) with deletion or mutation of TP53 have exceedingly poor clinical outcomes. Cenersen, an oligonucleotide targeting TP53, has been shown to abrogate the activity of TP53 gain-of-function mutants and to increase sensitivity of lymphoma cells to cytotoxic chemotherapy in vitro. We combined cenersen with fludarabine, cyclophosphamide and rituximab (FCR) as treatment for patients with high-risk CLL. The purpose of this phase II study was to determine the overall response rate, response duration and toxicity of cenersen administered in combination with FCR. Twenty patients with relapsed or high-risk CLL were evaluated. Nineteen patients were previously treated. The complete response rate was 18%; the overall response rate was 53%. Median progression-free and overall survival was 5.3 and 10.6 months, respectively. The most common serious adverse events were neutropenia and thrombocytopenia. In this single arm phase II study, cenersen combined with FCR yielded clinical responses with acceptable toxicity in patients with high-risk CLL.