Understanding the relationship between growth and proliferation in multicellular organisms requires identification of the key regulators of growth control, and an understanding of how they regulate growth and how growth is linked to cell proliferation. Recent progress in understanding the mechanisms of growth control indicates that the tuberous sclerosis complex tumour-suppressor TSC1-2 serves as a point of integration between growth-stimulatory and growth-suppressive signalling upstream of a small GTPase, Rheb. However, Rheb-induced growth might not explain the additional effects of TSC1-2 upon cell proliferation.