The impact of intraocular involvement (IOL) in primary CNS lymphoma (PCNSL) has not been sufficiently evaluated. Here, we present the analysis of IOL in the only completed randomized phase III trial in PCNSL. The G-PCNSL-SG1 study evaluated the role of whole-brain radiotherapy in primary therapy of PCNSL. Data of the 526 eligible study patients were checked, and clinical characteristics, therapy, and outcome of patients with IOL diagnosed at study inclusion were analyzed. Ophthalmologic examination at study inclusion was performed in 297 patients (56.5 %) of whom IOL was diagnosed in 19 (6.4 %). Clinical characteristics did not significantly differ between patients with IOL (IOL+) and those without (IOL-). The median progression-free survival (PFS) in the IOL+ group was 3.5 months (95 % CI 0.0-7.07) as compared to 8.3 months (95 % CI 4.78-11.78) in the IOL- group (P = 0.004), the median overall survival (OS) was 13.2 months (95 % CI 0.86-25.62) and 20.5 months (95 % CI 15.56-25.5), respectively (P = 0.155). In multivariate analysis, a significantly inferior PFS and OS for IOL+ patients were found. IOL at diagnosis of PCNSL was an independent negative prognostic indicator for PFS and OS in this analysis.