Background Cognitive deficits are a core feature of schizophrenia and are closely associated with poor functional outcomes. It remains unclear if cognitive deficits progress over time or remain stable. Determining patients at increased risk of progressive worsening might help targeted neurocognitive remediation approaches. Methods This 20-year follow-up study examined neurocognitive outcomes of 156 participants from the OPUS I trial. Neurocognition was assessed using the brief assessment of cognition in schizophrenia at the 10- and 20-year follow-up, allowing us to examine changes in neurocognition over ten years. Results We found that 30.5% of patients had a declining course of neurocognition, 49.2% had a stable course of neurocognition and 20.3% experienced improvements in neurocognition. Good cognitive functioning at the 20-year follow-up was significantly associated with higher levels of social functioning (B 6.86, CI 4.71-9.02, p < 0.001) while increasing experiential negative symptoms were significantly correlated to cognitive worsening (PC-0.231, p = 0.029). Younger age at inclusion (B: 0.23 per 10-years, CI 0.00-0.045, p = 0.047) and low level of education (below ten years) (mean difference: -0.346, CI -0.616 to -0.076, p = 0.012) predicted declining neurocognition. Conclusion Our findings support the notion of different schizophrenia subtypes with varying trajectories. Neurocognitive impairment at the 20-year follow-up was associated with other poor outcomes, highlighting the importance of treatments aimed at improving neurocognition in patients with schizophrenia spectrum disorders.