The location of sensory, somatic, and autonomic neurons projecting to the pig cremaster muscle (CM) was studied by means of the retrograde neuronal tracer Fast Blue (FB) technique. FB was randomly injected in the left CM of four impuberal pigs and serial sections of sensory and autonomic ganglia and spinal cord were examined under a fluorescence microscope. Additionally, some indications about the number and size of labeled neurons were given. Sensory pseudounipolar somata were located ipsilaterally in the L2–L6 and S1–S2 dorsal root ganglia, their total number ranging between 125 and 194, their mean diameter between 24 and 89 μm. Somatic multipolar motoneurons were located ipsilaterally in the L2–L4 neuromeres of the spinal cord, their total number ranging between 53 and 169, their mean diameter between 29 and 53 μm. Autonomic multipolar paravertebral ganglia neurons were located ipsilaterally from L1 to S4 and contralaterally from L2 to S2. Their total number ranged from 2,015 to 3,067 and their mean diameter between 25 and 55 μm. The multipolar caudal mesenteric ganglia neurons were located bilaterally, their total number ranging between 14 and 1,408 and their diameter from 22 to 39 μm. In two subjects only, multipolar neurons were also found ipsilaterally in the microganglia of pelvic plexus (2 and 13 neurons). Their mean diameter ranged between 28 and 54 μm. Our study documented that the CM-projecting neurons were located at different neural levels, with a predominance in the autonomic ganglia. Anat Rec Part A, 288A:1050–1058, 2006. © 2006 Wiley-Liss, Inc.