Differentiation of noradrenergic neurons from neural crest-derived precursors results in the formation of primary sympathetic ganglia. As sympathetic neurons continue to divide after the acquisition of adrenergic and neuronal properties it was unclear, whether the increase in neuron number during neurogenesis is due to neuron proliferation rather than differentiation of progenitor cells. Here, we demonstrate Sox10-positive neural crest progenitor cells and continuous sympathetic neuron generation from Phox2b-positive autonomic progenitors during early chick sympathetic ganglion development. In vivo activation of Notch signaling resulted in a decreased neuronal population, whereas expression of the Notch signaling inhibitor Su(H)(DBM) increased the proportion of Scg10-positive neurons. Similar results were obtained for sensory dorsal root ganglia (DRG). The effects of Notch gain- and loss-of-function experiments support the notion that progenitor maintenance and neuron differentiation from progenitor cells are essential for neurogenesis also during early sympathetic ganglion development.