Objective: To investigate, if neuromyelitis optica spectrum disorder (NMOSD) patients develop subclinical visual pathway impairment independent of acute attacks. Methods: 548 longitudinally assessed full-field visual evoked potentials (VEP) of 167 NMOSD patients from 16 centers were retrospectively evaluated for changes of P100-latencies and P100-N140-amplitudes. Rates of change in latencies (RCL) and amplitudes (RCA) over time were analyzed for each individual eye using linear regression and compared using generalized estimating equation models. Results: The rates of change in the absence of optic neuritis (ON) for minimal VEP intervals of ≥3 months between baseline and last follow-up were +1.951ms/year (N=101 eyes; SD=6.274; p=0.012) for the P100-latencies and -2.149µV/year (N=64 eyes; SD=5.013; p=0.005) for the P100-N140-amplitudes. For minimal VEP intervals of ≥12 months the RCL was +1.768ms/year (N=59 eyes; SD=4.558; p=0.024) and the RCA was -0.527µV/year (N=44 eyes; SD=2.123; p=0.111). The history of a previous ON >6 months before baseline VEP had no influence on RCL and RCA. ONs during the observational period led to mean RCL and RCA of +11.689ms/year (N=16 eyes; SD=17.593; p=0.003) and -1.238µV/year (N=11 eyes; SD=3.708; p=0.308), respectively. Conclusions: This first longitudinal VEP study of NMOSD patients provides evidence of progressive VEP latency delay occurring independently of acute ON. Prospective longitudinal studies are needed to corroborate these findings and help to interpret the clinical relevance.