MRI is the gold standard for treatment response assessment in glioblastoma. However, there is no consensus regarding the optimal interval for MRI follow-up during standard treatment. Moreover, reliable assessment of treatment response is hindered by the occurrence of pseudoprogression. It is unknown if a radiological follow-up strategy with 2-3 months intervals actually benefits patients and how it influences clinical decision making about continuation or discontinuation of treatment. This study assessed the consequences of scheduled follow-up scans (post-chemoradiotherapy [post-CCRT], after 3 cycles of adjuvant chemotherapy [TMZ3/6], after completion of treatment [TMZ6/6]) and unscheduled scans on treatment decisions during standard concomitant and adjuvant treatment in glioblastoma patients. Additionally, we evaluated how often follow-up scans resulted in diagnostic uncertainty (tumor progression versus pseudoprogression), and whether perfusion MRI improved clinical decision making. Scheduled follow-up scans during standard treatment in glioblastoma patients rarely resulted in early termination of treatment (2.3% post-CCRT, 3.2% TMZ3/6, and 7.8% TMZ6/6), but introduced diagnostic uncertainty in 27.7% of cases. Unscheduled scans resulted in more major treatment consequences (30%; p<0.001). Perfusion MRI caused less diagnostic uncertainty (p=0.021) but did not influence treatment consequences (p=0.871). This study does not support the current pragmatic follow-up strategy and suggests a more tailored follow-up approach.