The compressibility of manganese compounds with different structures and compositions (YMn2, Y6Mn23, YMn12, Y(Mn0.8Fe0.2)2 and ScMn2) was studied up to ≈40 GPa using a diamond anvil cell with synchrotron radiation. In the case of YMn2 we observed a very large compressibility which decreases considerably upon changing the atomic surrounding of the Mn atoms, as shown by the pseudobinary Y(Mn0.8Fe0.2)2 and ScMn2. The other two Y-Mn compounds Y6Mn23 and YMn12 also show enhanced compressibilities; however, they are not as large as that of YMn2. Thermal expansion data, which were also included in the discussion, show that the thermal expansion is closely related to the compressibility. The unusually large differences in the compressibility and the thermal expansion among the compounds investigated have been attributed to a different 'chemical pressure' acting on the Mn atoms, depending on the space available on the Mn sites in the different structures.