OBJECTIVE: To investigate sperm mitochondrial integrity through analysis of mitochondrial membrane potential (Δψ) and to correlate the energy status with variations in sperm motility. DESIGN: Experimental study. SETTING: Seminology Laboratory, University of Rome, Italy. PATIENT(S): Two hundred thirteen semen samples from the same number of patients, divided into two groups on the basis of their motility: group A, 185 samples with linear motility and group B, 28 samples with nonlinear motility. INTERVENTION(S): Evaluation of sperm motility. MAIN OUTCOME MEASURE(S): Sperm mitochondrial integrity evaluated with a fluorimetric method using the cationic lipophilic stain JC-1. RESULT(S): The mean FL2 (percentage of sperm with high and low ∆ψ) for group A was 46.19±23.25 and for group B, it was 48.32±24.43. There was no significant difference between the groups. There was a positive correlation between both FL2 and linear motility and FL2 and sperm vitality in group A; both correlations were statistically significant. In group B, there was a positive correlation between FL2 and nonlinear motility and FL2 and sperm vitality; again, both correlations were statistically significant. CONCLUSION(S): Our data reveal a positive correlation between total motility and Δψ, suggesting that sperm motility may be dependent on the functional integrity of the mitochondria.