The article presents a microstructural examination of neutron-irradiated tungsten (W), that was irradiated to four damage doses of 0.1 dpa, 0.2 dpa, 0.5 dpa and 0.8 dpa and at four temperatures of 600°C, 800°C, 900°C and 1200°C in the BR2 material test reactor (Mol, Belgium). The irradiation parameters cover a wide range that enables a comprehensive study of defect formation and evolution. The experimental work includes imaging and quantitative analysis of radiation induced voids and dislocation loops as well as the visualization of the distribution of the transmutation induced Re and Os. It demonstrates the dose- and temperature-dependent evolution of defect's size and number density as well as the segregation behavior of Re and Os at these defects. It was proven that the size of the defects increases, while their number density decreases with increasing damage dose. The formation of nanometer-sized Re–Os precipitates with elongated shape was detected in samples irradiated at 0.8 dpa. The large-scale EDX analysis showed the influence of grain and sub-grain boundaries as well as line dislocations on defect formation and thus on Re and Os-segregation behavior.