The reniform nematode, Rotylenchulus reniformis, was first reported in Arkansas in 1988. Incidence of this nematode in the state is greatest in cotton fields in east-central and southern Arkansas. In 1998, reniform nematodes were first detected in three fields in extreme northeastern Arkansas. While soil samples submitted to the Arkansas Nematode Diagnostic Laboratory from production fields in this area of the state indicate an increase in incidence of the reniform nematode in this region, nematode population densities are generally lower than population densities in the southern part of the state in the spring. An experiment to compare the over-winter vertical population dynamics of the reniform nematode from two cotton fields in northeast (MS) and east-central (MR) Arkansas was initiated in 2005. A parallel study was also initiated to compare the over-wintering age of the nematodes at three different times in the two cotton fields. Samples were collected vertically to a depth of 120 cm from each site in October, 2005 and in February and April, 2006. Each sample contained six 20-cm segments. Nematode densities were highest in the 20- to 40-cm segments at each sampling date, and densities decreased rapidly below 40 cm in both fields. Nematode age was determined by counting the number of cuticles on 100 random individuals from the 0- to 20-cm and 20- to 40-cm segments from each of the two fields. A greater number of nematodes that had one or more cuticles was recovered from the MS field than from the MR field, indicating that the nematodes from the MS field were younger at the time of sampling.