Evaluation of tolerability is increasingly relevant for patients with haematological malignancies treated with chronically administered therapies. Adverse events from these agents might affect the ability of patients to tolerate treatment over time. Conventional toxicity tables that include the incidence of high-grade adverse events, defined by the Common Terminology Criteria for Adverse Events, do not provide information on the time profile of these adverse events or reflect the continuous, lower grade symptomatic toxicities that are particularly relevant to treatment tolerability for patients living with indolent disease. Modern approaches to the evaluation and reporting of toxicity that capture the tolerability of treatment to the patient are imperative. In this Viewpoint, we present a focused, pilot, and longitudinal Toxicity over Time analysis of adverse events from lenalidomide and lenalidomide with rituximab in patients with follicular lymphoma treated in the CALGB 50401 (Alliance; NCT00238238) trial to define the trajectory of adverse events and quantify the burden of continuous, low-grade events. Toxicity over Time analyses provided clinically relevant descriptions of neutropenia and fatigue trajectories caused by lenalidomide that were not identified by standard analysis of the maximum grade events defined by the Common Terminology Criteria for Adverse Events. Systematic, rigorous incorporation of patient-reported outcomes in clinical trials will be crucial to our understanding of the tolerability of chronically administered therapies in patients with haematological malignancies.