Neurocysticercosis is a world public health problem. An increase in immunoglobulin G (IgG) concentration in the cerebrospinal fluid of patients with neurocysticercosis has been described but the reasons for this finding are unknown. Our hypothesis is that the increase in IgG concentration in cerebrospinal fluid is due to exclusive intrathecal synthesis of IgG and this process is associated with the inflammatory phases of the disease. We studied IgG concentration in cerebrospinal fluid in 16 patients with neurocysticercosis comparing with a control group of 19 patients to verify which pattern of increase in IgG concentration in cerebrospinal fluid occurs in neurocysticercosis. In the neurocysticercosis group, intrathecal synthesis of IgG was detected in 12 (75%) and 5 (31.2%) patients by quantitative and qualitative methods, respectively. When compared with the control group the neurocysticercosis patients had the same pattern of intrathecal synthesis of IgG as multiple sclerosis patients. Intrathecal synthesis of IgG was not associated with any variable indicative of an inflammatory process. We conclude that the increase in IgG concentration in neurocysticercosis is due to intrathecal synthesis, as is also the case for multiple sclerosis, and that this process is not related to the inflammatory stage of NCC.