The fibroblast growth factor (FGF) pathway is active in several cell types within the developing cerebellum. During early embryogenesis, FGF signalling helps to establish cerebellar territory but its function during later development is unclear. Now, on p. 2957, M. Albert Basson and colleagues report that the normal development of several cell types in the mouse cerebellum depends on tight regulation of FGF signalling by sprouty genes, which encode feedback antagonists of FGF signalling. Spry1, Spry2 and Spry4 are expressed in the developing cerebellum. The researchers show that simultaneous deletion of multiple sprouty genes results in numerous cerebellar defects, including abnormal folding of cell layers and reduced granule cell proliferation. Reducing the Fgfr1 dosage rescues these abnormalities, confirming that they are due to excess FGF signalling. Moreover, the effects of deregulated signalling on cerebellar morphology depend on the time and cell type in which sprouty genes are deleted. Thus, suggest the researchers, FGF signalling has several distinct functions and must be tightly controlled during cerebellar morphogenesis.