A medical system implements a seizure detection algorithm to detect a seizure based on a first patient parameter. The medical system monitors a second patient parameter to adjust the seizure detection algorithm. In some examples, the medical system determines whether a seizure for which therapy delivery is desirable occurred based on a second patient parameter. If a target seizure occurred, and the seizure detection algorithm did not detect the target seizure, the medical system adjusts the seizure detection algorithm to detect the target seizure. For example, the medical system may determine a first patient parameter characteristic indicative of the target seizure detected based on the second patient parameter and store the first patient parameter characteristic as part of the seizure detection algorithm. In some examples, the first patient parameter is an electrical brain signal and the second patient parameter is patient activity (e.g., patient motion or posture).