Glomerular filtration rate (GFR) assessment is indicated before every administration of cisplatin. The optimal modality for this purpose [GFR measurement by urinary Creatinine Clearance (uCrCl) versus GFR estimation (eGFR) by the CKD-EPI formula versus both] is unclear. We investigated whether eGFR only is safe in this setting. Paired uCrCl and eGFR determinations from 470 cisplatin cycles from 121 patients were analyzed [median age: 55 years; most frequent tumor site: genitourinary (45%); palliative treatment: n = 41 (34%)]. Primary endpoint was the proportion of cycles with uCrCl < 50 ml/ min/1.73m 2 and eGFR ≥ 50 ml/min/1.73m 2 (i.e. a "false negative" result when only determining eGFR). The primary endpoint occurred in 8 of 470 cisplatin cycles (1.7%, 95%CI 0.5-2.9). In all 8 events, uCrCl was lower than eGFR (mean uCrCl vs. eGFR: 43 versus 112 ml/min/1.73m 2). The uCrCl was re-measured in all patients, and showed normal results in all but 1 patient. None of these events precluded the administration of cisplatin at the planned date, and no subsequent cases of acute nephrotoxicity occurred. Overall agreement between uCrCl and eGFR was low, with qualitative analysis suggesting frequent incompliance with 24-h urine collection. We conclude that an eGFR is sufficient for assessing kidney function in patients with cancer undergoing cisplatin therapy. Cisplatin is a widely-used antineoplastic drug that is essential for the therapy of a broad range of solid and hematologic cancers in children 1 , adolescents 2 , and adults 3,4. Acute kidney injury (AKI) is a rare but potentially life-threatening complication of cisplatin therapy 5. Because this complication occurs predominantly in patients with already pre-existing kidney dysfunction, cisplatin is widely considered to be contraindicated in patients with a glomerular filtration rate (GFR) below 50-60 ml/min/1.73m 26,7. To identify these patients, a pre-treatment evaluation of kidney function by determining the GFR is mandatory in every patient before every cisplatin administration 8. However, it is unclear which method of GFR assessment is optimal for this purpose, with some centers opting for (1) a GFR measurement by urinary Creatinine Clearance (uCrCl), (2) an estimated GFR by a validated formula such as CKD-EPI (eGFR), or (3) both 9. The uCrCl has the advantage of being the potentially most accurate routinely-available method of GFR assessment ("gold standard", ignoring non-routinely available