The electrophysiological mechanisms of human memory encoding and recall are incompletely understood. Precise interaction of single-neuron activity and brain oscillations presumably play a critical role in this process. Here, we used human single-neuron recordings from an object-location memory task with separate periods for encoding and retrieval to analyze the timing of single-neuron activity in the medial temporal lobe relative to the local theta rhythm. 18 epilepsy patients participated in the task and contributed to 27 experimental sessions. We extracted single-neuron action potentials from hybrid depth electrode recordings using the spike-sorting algorithm Wave_clus and computed the generalized phase of the bandpass filtered local field potential (1-10 Hz) to estimate the instantaneous theta phase of each spike. For each neuron, we then applied a Watson-Williams test to compare the phase distribution of action potentials between encoding and retrieval. We found that a significant portion of the recorded neurons phase locked to the theta rhythm, similarly during encoding and retrieval of memories. Neurons generally locked to the trough of theta oscillations, replicating previous observations. Theta-phase locking was most prevalent during periods with high theta power. In some of the phase-locked neurons, we observed small but significant shifts in the preferred phases between encoding and retrieval, which is in line with theoretical models predicting separate phases for encoding and retrieval. Our results suggest that human memory recall involves specific timing of single-neuron action potentials of individual neurons relative to the theta rhythm during both memory encoding and retrieval.