BACKGROUND AND PURPOSE: Propofol is a cerebral vasoconstrictor that modulates cerebral perfusion by decreasing the metabolic rate of oxygen. Because younger children often undergo intravenous sedation for MR imaging, this study set out to evaluate the degree of leptomeningeal contrast enhancement on 3T postcontrast brain MR imaging and to determine whether this phenomenon relates to sequence, sedation dosage, or patient age or weight. MATERIALS AND METHODS: During a 2-year period, of 152 children 1-5 years of age who underwent MR imaging, 43 were included for MRI review. Of these, 37 underwent postcontrast imaging with either solely gradient-echo T1WI (n 20) or spin-echo T1WI (n 17); notably, 6 patients underwent both sequences. Three neuroradiologists separately graded the degree of leptomeningeal contrast enhancement (grades 0 -3) that was correlated with various factors and calculated the interobserver reliability. RESULTS: For the 43 patients, the mean patient age was 3.1 1.4 years. The leptomeningeal contrast-enhancement grade was significantly greater (P .0001) on spin-echo T1WI (1.9 -2.1) versus gradient-echo TIWI (1.2-1.4). Patient weight (r 0.366 to .418, P .003-.01) and age (r 0.315 to 0.418, P .004 -.032) moderately and inversely correlated with the leptomeningeal contrast-enhancement grade, while the propofol dosage, sedation duration, and time to T1WI post-contrast administration did not (each, P .05). The interobserver was strong regarding the leptomeningeal contrast-enhancement grade on both spin-echo T1WI ( 0.609 - 0.693, P .0001) and gradient-echo TIWI ( 0.567- 0.698, P .0001). CONCLUSIONS: Leptomeningeal contrast enhancement (or “pseudo”-leptomeningeal contrast enhancement) occurs with a greater frequency and degree on 3T postcontrast spin-echo T1WI relative to gradient-echo TIWI in younger children sedated with propofol and should not be mistaken for disease. This phenomenon may be more prominent with lower age or size and may arise from propofol-induced vascular smooth-muscle dilation.