Hematological malignancies comprise a diverse group of tumors that affect the blood, bone marrow and lymph nodes, and account for around 8% of all malignancies diagnosed annually in the Netherlands. Hematological malignancies of myeloid origin that predominantly affect the elderly include, but are not limited to, myelodysplastic syndromes (MDS), chronic myelomonocytic leukemia (CMML) and acute myeloid leukemia (AML). These myeloid malignancies are related, albeit distinct, disease entities and are diagnosed in around 65, 70 and 45% of people above the age of 70, respectively. Despite that they are frequently diagnosed among older adults, they are commonly excluded, or underrepresented in clinical trials. Therefore, findings from clinical trials may not be generalizable to the entire older patient population. As a result, optimal diagnostic and treatment approaches for this elderly population are based on insufficient evidence and remain controversial. In addition, clinical trials do not and cannot provide a complete picture of the overall characteristics of patients at the population level. The main aim of this thesis is to progress our understanding on different epidemiologic aspects of myelodysplastic syndromes (MDS), chronic myelomonocytic leukemia (CMML) and acute myeloid leukemia (AML) at the population level in the Netherlands. These aspects include surveillance of the cancer burden, guideline adherence concerning diagnostics and therapy, and comparative effectiveness research. Population-based registries are useful instruments to study all patients within a well-defined area, so as to overcome patient selection which is always at hand in clinical intervention studies. The work described in this thesis utilizes three Dutch population-based registries to unravel real-world characteristics and management of patients with MDS, CMML and AML, namely (i) the nationwide population-based Netherlands Cancer Registry (NCR), (ii) the Dutch medical claims-based DBC Information System and (iii) the Dutch ...