Purpose: The purpose of this study was to investigate the potential of [1-¹¹C]acetate (AC) as a metabolic tracer for renal cell cancer in human subjects. Methods: Twenty-one patients with suspected kidney tumours were investigated with AC and dynamic PET. AC uptake was scored on a five-step scale. Tumour localisation was known from CT/MRI. Histology was available in 18/21 patients. The results in these 18 patients are reported. Results: AC uptake by the tumour was less than (n = 11), equal to (n = 5) or higher than (n = 2) uptake in the surrounding renal parenchyma. Histological tumour types showed a typical distribution, with a predominance of clear cell carcinomas (n = 14) and only a small number of papillary cell carcinomas (n = 2) and oncocytomas (n = 2). Only the benign oncocytomas were highly positive with AC. Conclusion: In most kidney tumours the AC accumulation was not higher than in normal kidney parenchyma. Therefore, AC PET cannot be recommend for the characterisation of a renal mass.