Changes in cell mass in atherosclerosis represent changes in cell division, cell death and migration/emigration, all of which may be occurring simultaneously in different cell types at different times and in different regions of the plaque. This makes measurement of these individual processes and measurement of overall cell kinetics in atherosclerosis difficult, with the challenges and shortfalls only recently becoming apparent. This review will outline the problems associated with assaying cell proliferation and cell death, and how these processes relate to changes in overall cell kinetics and measurement of biological age.Cell division and cell death have historically been assayed as frequencies of specific processes, with at times ill-defined and nonspecific markers. More recent studies have moved towards cumulative assays that can measure overall rates over time, resulting in a 'biological' age or replication history of a tissue or cell.The complexity of processes involved in assaying changes in cell kinetics in atherosclerosis mean that we must move towards cumulative assays of cell proliferation, cell death and senescence that can be measured in the time frames over which atherosclerosis occurs, and for studies that selectively manipulate one of these processes in a single-cell type without affecting other processes.