We report the discovery of a very diverse set of five low-surface brightness (LSB) dwarf galaxy candidates in Hickson Compact Group 90 (HCG 90) detected in deep U- and I-band images obtained with Very Large Telescope/Visible Multi-Object Spectrograph. These are the first LSB dwarf galaxy candidates found in a compact group of galaxies. We measure spheroid half-light radii in the range 0.7 ... r sub( eff)/kpc ... 1.5 with luminosities of -11.65 ... M... -9.42 and -12.79 ... M sub( I) ... -10.58 mag, corresponding to a colour range of (U - I) sub( 0) ... 1.1-2.2 mag and surface brightness levels of ... 28.1 mag arcsec super( -2) and ... 27.4 mag arcsec super( -2). Their colours and luminosities are consistent with a diverse set of stellar population properties. Assuming solar and 0.02...Z... metallicities we obtain stellar masses in the range M*... 10 super( 5.7 - 6.3) M... and M*... 10 super( 6.3-8) M... Three dwarfs are older than 1 Gyr, while the other two significantly bluer dwarfs are younger than ~2 Gyr at any mass/metallicity combination. Altogether, the new LSB dwarf galaxy candidates share properties with dwarf galaxies found throughout the Local Volume and in nearby galaxy clusters such as Fornax. We find a pair of candidates with ~2 kpc projected separation, which may represent one of the closest dwarf galaxy pairs found. We also find a nucleated dwarf candidate, with a nucleus size of r sub( eff) ... 46-63 pc and magnitude M sub( U, 0) = -7.42 mag and (U - I) sub( 0) = 1.51 mag, which is consistent with a nuclear stellar disc with a stellar mass in the range 10 super( 4.9 - 6.5) M... (ProQuest: ... denotes formulae/symbols omitted.)