The scope of this paper is to perform a detailed spectroscopic study of the northern O-type supergiant HD 195592 .
We use a large sample of high quality spectra in order to investigate its multiplicity , and to probe the line profile variability .
Our analysis reveals a clear spectroscopic binary signature in the profile of the He i \lambda 6678 line , pointing to a probable O + B system .
We report on low amplitude radial velocity variations in every strong absorption line in the blue spectrum of HD 195592 .
These variations are ruled by two time-scales respectively of 5.063 and about 20 days .
The former is firmly established , whilst the latter is poorly constrained .
We report also on a very significant line profile variability of the H \beta line , with time scales strongly related to those of the radial velocities .
Our results provide significant evidence that HD 195592 is a binary system , with a period that might be the variability time-scale of about 5 days .
The second time scale may be the signature of an additional star moving along a wider orbit provided its mass is low enough , even though direct evidence for the presence of a third star is still lacking .
Alternatively , the second time-scale may be the signature of a variability intrinsic to the stellar wind of the primary , potentially related to the stellar rotation .