Serotonin-immunoreactive neurons were identified in the central nervous system (CNS) of Anastrepha obliqua Macquart, 1835 wandering stage larvae. The PAP immunocytochemical method was applied to the entire CNS (whole mounts). About 90 neurons were visualized in the CNS (20 in the brain and 70 in the ventral ganglion). Both somata and axons were strongly stained. These neurons showed a segmental arrangement and bilateral symmetry. All processes presented a basic projection pattern, in which the major fibres travel contralaterally. Comparison of these neurons with serotonergic neurons described in other insects suggests order-specific traits such as cerebral clusters and presence of only one 5-HT immunoreactive neuron in the 8th abdominal neuromere as well.