Progression of degeneration is often described in patients with initially degenerated segment adjacent to fusion (iASD) at the time of surgery. The aim of the present study was to compare dynamic fixation of a clinically asymptomatic iASD, with circumferential lumbar fusion alone. 60 patients with symptomatic degeneration of L5/S1 or L4/L5 (Modic ≥ 2°) and asymptomatic iASD (Modic = 1°, confirmed by discography) were divided into two groups. 30 patients were treated with circumferential single-level fusion (SLF). In dynamic fixation transition (DFT) patients, additional posterior dynamic fixation of iASD was performed. Preoperatively, at 12 months, and at a mean follow-up of 76.4 (60-91) months, radiological (MRI, X-ray) and clinical (ODI, VAS, satisfaction) evaluations assessed fusion, progression of adjacent segment degeneration (PASD), radiologically adverse events, functional outcome, and pain. At final follow-up, two non-fusions were observed in both groups. 6 SLF patients and 1 DFT patient presented a PASD. In two DFT patients, a PASD occurred in the segment superior to the dynamic fixation, and in one DFT patient, a fusion of the dynamically fixated segment was observed. 4 DFT patients presented radiological implant failure. While no differences in clinical scores were observed between groups, improvement from pre-operative conditions was significant (all p < 0.001). Clinical scores were equal in patients with PASD and/or radiologically adverse events. We do not recommend dynamically fixating the adjacent segment in patients with clinically asymptomatic iASD. The lower number of PASD with dynamic fixation was accompanied by a high number of implant failures and a shift of PASD to the superior segment.