Objective: There are some mixed cysts (MC) with overlapping histological features of aneurysmal bone cyst (ABC) and simple bone cysts (SBC). Method: We reviewed 69 pure ABC, 40 SBC and 23 "Mixed Cysts (MC)", and compared them by nonparametric tests. Results: MCs, mainly showed two paterns as "Type 1: SBC with secondary ABC foci (n=18)"and "Type 2: Cysts with fully developed SBC and ABC areas (n=5)". The median age for ABC, SBC, and MC were 16±18.2 (range: 3-53), 21±13.7 (range: 3-54) and 9±11.47 years old (range: 3-50) respectively. MCs were more frequent in males than ABC and SBC (p=0.017) and the most frequently involved bones were humerus-femur-pelvic bones in descending order (p= 0,021). "Type 1 MC" showed more frequent cementum-like amorph material (p<0.001), ectatic venules (p=0.040), calcifications (p=0.044), less cholesterol deposition, necrosis and no different fracture and osteoid matrix when compared with Type 2 MCs and SBCs. Conclusion: Cysts with overlapping features of ABC and SBC are not uncommon. Though they usually represent "SBCs with secondary ABC component", they have dissimilarites with ordinary SBCs which needs to be further clarified with larger series. Objective: Percent of tumor necrosis after neoadjuvant chemotherapy, determined by detailed specimen mapping, has a high prognostic value. However both the mapping and grading systems has some practical problems. Method: 128 cases were reviewed for potential pitfalls in handling and reporting processes and correlated with radiological findings by nonparametric-tests. Results: Most of the tumors were osteosarcoma (74.2 %) and Ewing Sarcoma (16.4 %), located in femur (53 %), tibia (22,7 %) and humerus (10.2 %). Cortex, soft tissue and joint invasion was observed in 94 %, 77.6 % and 30.3 % of the cases, respectively. A median of 27.5 tumor blocks (9-74± 14,64) were submitted for histology. Tumors were totally necrotic in 30 cases (24 %) (Huvos Grade-HG-IV), HG III in 20.3 %, HG II in 28.1 % and HG I in 24.2 % of the cases. Overall good (HG III-IV) and poor responders (HG I-II) correlated well with radiological findings (p<0.001). Discrepant cases showed extensive oedema and congestion enhancing contrast medium, patchy necrosis unabling accurate histologic evalation, or failure to prove tibiofibuler joint involvement because of sagittal sectioning (p<0.05).