Photoelectric, photographic and CCD UBV photometry, spectroscopic observations and star counts are presented for the open cluster Berkeley 58 to examine a possible association with the 4.37 d Cepheid CG Cas. The cluster is difficult to separate from the early-type stars belonging to the Perseus spiral arm, in which it is located, but has reasonably well-defined parameters: an evolutionary age of ∼108 yr, a mean reddening of E(B−V) (B0) = 0.70 ± 0.03 s.e. and a distance of 3.03 ± 0.17 kpc (V0−MV= 12.40 ± 0.12 s.d.). CG Cas is a likely cluster coronal member on the basis of radial velocity, and its period increase of +0.170 ± 0.014 s yr−1 and large light amplitude describe a Cepheid in the third crossing of the instability strip lying slightly blueward of strip centre. Its inferred reddening and luminosity are E(B−V) = 0.64 ± 0.02 s.e. and 〈MV〉=−3.06 ± 0.12 . A possible K supergiant may also be a cluster member.