We describe the structural principles of two novel families of cage hydrocarbons: icosahedral fulleranes and diarnondoids. Quantum chemical calculations are performed for the fulleranes and the diamondoids up to C980H980 and C1100H300 in size. The fulleranes are significantly stabilized by partial endo-hydrogenation, resulting in remarkably stable hollow (CH)(n), cages. The structural principles of the icosahedral diamondoids can be derived from multilayered fulleranes. Thermodynamic stabilities of the icosahedral diamondoids are verified by comparisons to crystalline forms of hydrocarbons together with the conventional octahedral diamondoids uP to C969H324. Spectral features of the fulleranes and diamondoids are analyzed from the perspectives of their possible existence in space and structural characterization. The described structural motifs of the fulleranes and diamondoids are expected to aid in identification and characterization of the experimentally known hydrocarbon and diamond nanostructures.