In the brain of adult rodents, young neurons arising from the subventricular zone (SVZ) of the lateral ventricle migrate tangentially along the rostral migratory stream (RMS) toward the olfactory bulb. The aim of this study was to determine whether surgical lesions placed through the RMS could affect the rostral migration of these newly formed neurons. Confocal and electron microscopy were used to characterize their anatomical organization within the intact and lesioned forebrains. As soon as 7 days and up to 45 days after placing a surgical lesion through the proximal portions of the RMS, numerous cells immunostained for polysialylated neural cell adhesion molecule (PSA-NCAM) were detected both (1) throughout the lesional cavity extending from the cortex to the anterior commissura, and (2) within the tissue located caudal to the lesion. In both regions, these PSA-NCAM-immunostained cells were labeled for neuronal markers but were negative for glial fibrillary acidic protein (GFAP). After administration of the proliferation marker bromodeoxyuridine (BrdU), nuclear labeling was associated with cells immunostained for PSA-NCAM but GFAP-negative, that accumulated within the lesional cavity and in the tissue caudal to the lesion. For the longest postlesional delays, a number of the PSA-NCAM-immunostained neurons located in various portions of the lesional cavity exhibited intense immunostaining for gamma-aminobutyric acid, whereas only a few of them exhibited faint immunostaining for tyrosine hydroxylase. These data indicate that surgical lesions placed through the RMS of adult rats impede the migration toward the olfactory bulb of the neuroblasts arising from the SVZ, inducing their accumulation and their partial differentiation in forebrain regions caudal to the lesion.