OBJECTIVES: The study aimed to develop a standardized scale for co-morbidity assessment in Chronic Lymphocytic Leukaemia (CLL) patients to support physicians for selecting  the optimal treatment according to the patient co-morbidity profile METHODS: The co-morbidity scale was developed in four steps: a literature review to assess the existence of other scales and define the scale content; consensus meetings with five CLL experts to determine the content, format and weighting factor for each co-morbidity ; a pilot study of 10 CLL patients to assess the scale feasibility; a meeting to agree the final version RESULTS: The literature review did not identify any existing scale but six papers related to assessment of CLL co-morbidities were selected. These allowed the initial selection of 21 diseases. In the expert meeting, the scale was reduced to 13 co-morbidities, with major impact on CLL treatment selection. Some additional variables (age, patient dependence and ECOG performance status) were added. Subsequently, the final list of co-morbidities. variables and response options were agreed. The experts applied a weight factor to each co-morbidity, from 1 (minimal importance) to 3 (very important). A pilot study of 10 patients, using an electronic version of the scale, resulted in some changes but confirmed the scale’s feasibility. The final scale includes three sections. Part 1, the Functional Vital Scale, and a global assessment of the patient (not included in the global score). Part 2, the Co-morbidity scale, including 11 co-morbidities weighted from 0 to 2 and scored from 0 (absence) to 2 (severe co-morbidity). Part 3, CLL alerts, is descriptive and includes the presence of splenectomy and hypogammaglobulinemia. CONCLUSIONS: The co-morbidity scale is a tool to support the clinician in the selection of the optimal treatment for CLL patients. Further research is required to validate the scale and assess its benefits.