To determine the prognostic value of myoclonic jerk in children with enterovirus 71 (EV71) infection, a retrospective study was conducted on 665 enterovirus culture-confirmed patients admitted to Chang Gung Children's Hospital from January 2000 to September 2001. The mean age was 35.0 months +/- 32.2 months, ranging from 1 day to 15 years and 416 (62.6%) of them were male. Among these patients, 140 (21.1%) had EV71 isolated, and 150 (22.6%) had myoclonic jerk. Fifty one percent (72/140) of EV71 cases and only 15% (78/525) of non-EV71 cases had myoclonic jerk (p<0.001). The age of enterovirus patients with myoclonic jerk was younger than that of patients without myoclonic jerk (23.2 +/- 17.6 vs 38.4 +/- 34.6 months, p=0.005). The hospitalization and fever durations were significantly longer in the EV71 group than in the non-EV71 group (8.3 +/- 13 vs 4.2 +/- 2.7 days, p<0.001; 5.9 +/- 4.8 vs 4.2 +/- 3.0 days, p=0.009, respectively). Patients with myoclonic jerk also had higher percentages of severe illness, and neurologic sequelae (20% and 9%, respectively) than those without myoclonic jerk (5% and 1%, respectively) [p<0.001]. The positive predictive values of myoclonic jerk for EV71 infection, severe cases, and neurologic sequelae were 0.48, 0.20, and 0.09, respectively; the negative predictive values for severe cases and neurologic sequelae were 0.95 and 0.99, respectively. This study demonstrated that myoclonic jerk and EV71 infection are both independently associated with more severe disease and higher incidence of neurologic sequelae.