Aims: In spiny dendrites of cerebellar Purkinje neurons, repetitive stimulation of afferent parallel fibers (PFs) induces sustained calcium signals, which are thought to trigger the induction of certain forms of long-term depression (LTD; Eilers et al., Learning & Memory, 1997). These calcium signals remain relatively constant both in their amplitude as well as in their spatial extend during ongoing synaptic activity. Methods: We analyzed the spatial profile of these calcium signals with a combination of imaging experiments and mathematical approximations. Results and Conclusion: At the border between active and inactive dendrites, the intracellular calcium concentration forms a gradient that drops e-fold from ~600 nM to resting values over 3.8 mm. Given the high concentration of the mobile endogenous calcium buffers calbindin and parvalbumin, such steep gradients were rather unexpected. However, our analysis predicts that neither the exogenous calcium indicator dye nor endogenous buffers significantly influence the shape of the calcium gradient. Instead, the capacity of dendritic calcium clearance mechanisms determines the steepness of the gradient and, correspondingly, the spread of dendritic calcium signals. Supported by DFG (GRK 1097)