Existing work emphasizes the importance of traffic congestion externalities, but typically ignores cruising-for-parking externalities. We estimate the marginal external cruising costs of parking—that is, the time costs that an additional parked car imposes on drivers by inducing them to cruise for parking—which is one of the main components of cruising-for-parking externalities. The level of cruising is identified by examining to what extent the car inflow rate into a parking location falls with parking occupancy level. For a commercial street in Istanbul, we demonstrate that a marginal car parking for an hour induces 3.6 other cars to cruise for parking. This translates into an external cruising cost that is in the same order of magnitude with the external traffic congestion cost created by the trip.