Abstract: Introduction. Epidemics of meningoencephalitis due to echovirus 9 were commonly occurred when a children population become susceptible for the first time in front the virus. Objective. To present the intrathecal synthesispattern of immunoglobulins of the epidemic that affected Cuba in 1999 and to probe the usefulness of reibergram and antibody index in the diagnostic and characterization ofthe outbreak Patients and methods. 23 pediatric patients suflering from viral meningoencephalitis due to echovirus 9 were studied in the income moment. Serum and cerebrospinal fluid IgA, IgM, IgG, albumin and glucose were quantified. Cerebrospinal fluid total protein content and lactate were quantified. Titles of antibodies against echo 9 and Coxsackie A 9 and differential cell count were performed. Results. A mean of 555 cells/10 - 6 L mainly lymphocytes were obtained. Glucose in cerebrospinal fluid was over 50%, serum glucose and lactate levels below 2.1 mmol/L. In the reibergram an absence of intrathecal synthesis was predominant (15/23), IgMsynthesis (6/23) and IgM+IgA (2/23). Blood-cerebrospinal fluid dysfunction was observed in 15 patients. The mean antibody index was 1,8 for echo 9 and 0,9 for Coxsackie A 9 - Conclusions. The intrathecal synthesis pattern of immunoglobulins was different from other enterovirus and from echovirus 9 in non-epidemic situations before this epidemic, probably with alteration ofviral genome.