Tricarbonyl-1,6-methanocyclodecapentaenechromium crystallises in the monoclinic spacegroup I2/a with eight molecules in a unit cell of dimensions a 13·38 ± 0·03, b 7·19 ± 0·02, c 24·72 ± 0·04 Å, β 94°35′± 10′. The structure has been determined from 749 visually estimated intensities and refined by least-squares fit. The final R value is 5·4%. The structure consists of discrete molecules of formulae C₁₄H₁₀O₃Cr. The structure is compared with that of 1,6-methanocyclodecapentaene-2-carboxylic acid and it is concluded that the delocalised π-electron system associated with the latter is maintained in the complex.