From HIV/syphilis co-infected patients with or without neurological symptom, those who had neurological symptoms, CD4 <350 per μL and serological TRUST titer ≥1:16 were 4.9-fold (95% confidence interval [CI]: 2.37–10.31), 4.3-fold (95% CI: 1.17–15.78), and 4.1-fold (95% CI: 1.58–10.76), respectively, more likely to be diagnosed with neurosyphilis. Here, CD4 is linked to neurosyphilis.