Quantum dots (QDs) are a class of semiconductor nanoparticles that possess a unique set of size-tunable optical properties. The potential applications of QDs in biological and medical applications are enormous, and include high-resolution cellular imaging, cancer tumour targeting and drug delivery. However, the mechanisms for QD-cell interactions are at best partially understood, and QD cytotoxicity is an ongoing concern. In particular, it remains unclear how QD uptake by cells and subsequent cell fate are influenced by QD parameters such as size, composition, concentration, and exposure time. We present a mathematical model that describes the toxic effects of QDs on cells. The model consists of a system of ordinary differential equations describing the transition of healthy cells to an apoptotic or necrotic state induced by QD toxicity. Directions for future development of the model are also identified.