Purpose There is a continuous search for imaging techniques with high sensitivity and specificity for brain tumors. Positron emission tomography (PET) imaging has shown promise, though many PET agents either have a low tumor specificity or impractical physical half-lives. 124 ICLR1404 is a small molecule alkylphosphocholine analogue that is thought to bind to plasma membrane lipid rafts and has shown high tumor-to-background ratios (TBR) in a previous pilot study in brain tumor patients. This study attempts to define the clinical value of 124 ICLR1404 PET/CT (aka CLR124). Procedures Adult patients with new or suspected recurrence of high-grade primary or metastatic brain tumors ( N  = 27) were injected with 124 ICLR1404 followed by PET/CT at 6, 24, and 48 h. Standard uptake values (SUV) and TBR values were calculated for all time points. Uptake of 124 ICLR1404 was qualitatively assessed, compared with magnetic resonance imaging (MRI), and correlated with clinical outcome. Final diagnosis ( N  = 25) was established based on surgically resected tissue or long-term follow-up. Results Positive uptake with high TBR was detected in all but one patient with a final diagnosis of primary/recurrent brain tumor (12/13) and in less than half of patients with treatment-related changes (5/12). Concordance between 124 ICLR1404 uptake and contrast enhancement on MRI was seen in < 40 %, with no concordance between T 2 -hyperintensities and uptake. No significant difference in overall outcome was found between patients with and without 124 ICLR1404 uptake. Conclusions The uptake pattern in these patients suggests a very high sensitivity of 124 ICLR1404 PET/CT for diagnosing tumor tissue; however, tumor specificity needs to be further defined. Relative lack of concordance with standard MRI characteristics suggests that 124 ICLR1404 PET/CT provides additional information about brain tumors compared to MRI alone, potentially improving clinical decision-making.