Delta-9-tetrahydrocananbinol (THC), the primary psychoactive ingredient in cannabis sativa, is a cannabinoid system receptor (CB1) agonist. Consistent with psychomotor disturbances associated with cannabis intoxication, accumulating evidence has implicated the CB1 receptor in mediating cerebellar cortical plasticity. This plasticity is postulated to be necessary in cerebellar-dependent associative learning as indexed by condition response (CR) acquisition and timing in the eyeblink conditioning (EBC) procedure. The current research investigated the performance of heavy cannabis users (n = 26, short-delay; n = 13, long-delay) and cannabis naive controls (n = 14, short-delay; n = 17 long-delay) in the EBC procedure using both short (400 ms)- and long (900 ms)-duration condition stimulus tones. Urine levels of THC and the inactive metabolite THC-COOH were assessed and EEG was recorded at FCz to examine event-related brain potential correlates of attentional processing during the EBC tasks. Heavy cannabis users (positive urine test) and controls were free of DSM axis I or axis II disorders, aside from cannabis abuse or dependence for users. Results indicated that cannabis users demonstrated impaired acquisition and timing of the CR in the short-delay EBC task, but did not differ from controls in the long-EBC task. Neither cannabis use rates nor analyte levels were associated with primary EBC performance variables (CR acquisition or timing). However, analyte levels were positively correlated with self-reported recreational cannabis use, particularly in the past week. These data extend a prior study of short-EBC in cannabis users and support the prevailing theory that long-term exposure to cannabinoid agonists likely instigates compensatory changes in the cannabinoid system, which in turn, alters CR-timing related cerebellar plasticity. Findings are used to refine the cannabinoid EBC model, with a particular focus on cerebellar cortical inhibitory interneurons.