Purpose Non-diagnostic results still hinder the routine use of core biopsy (CB) and fine needle aspiration (FNA) in the diagnostic process of renal tumours. Furthermore, substantial interobserver variability has been reported. We assessed the added value of combining the results of CB and FNA by five pathologists in the ex vivo diagnosis of renal mass. Methods Two ex vivo core biopsies were taken followed by two FNA passes from extirpated tumours. All samples were evaluated by five blinded pathologists. A consensus diagnosis of the surgical specimen was the index for comparison. For each pathologist, the number of non-diagnostic (non-conclusive or undetermined biology and failed biopsies), correct and incorrect scored cases of each technique was assessed. When a non-diagnostic CB or FNA had a correct diagnostic counterpart, this was considered as of added value. Results Of the 57 assessed tumours, 53 were malignant. CB was non-diagnostic in 4–10 cases (7–17.5%). FNA established the correct diagnosis in 1–7 of these cases. FNA was non-diagnostic in 2–6 cases (3.5–10.5%), and the counterpart CB established the correct diagnosis in 1–6 of these cases. For the 5 pathologists, accuracy of CB and FNA varied between 82.5–93% and 89.5–96.5%, respectively. Combination of both types of biopsy resulted in 55–57 correct results (accuracy 96.5–100%), i.e., an increase in accuracy of 3.5–14%. Conclusion Combining the result of CB and FNA in renal mass biopsy leads to a higher diagnostic accuracy. Recommendations on which technique used should be adapted to local expertise and logistic possibilities.