The selection effects that govern the observations of Visual Binary Stars are investigated, in order to obtain a realistic statistical distribution of the mass-ratioq=Msec/Mprim. To this end a numerical simulation programme has been developed, which ‘generates’ binary stars and ‘looks’ at them to determine whether an observer on Earth would be able to detect them. The simulations show that for mass-ratiosq>0.35, observations are expected to reveal the realq-distributions, while for mass-ratiosq<0.35 selection effects begin to play a major part. It is found that the observed mass-ratio distribution for Main-Sequence systems, derived from theIndex Catalogue of Visual Binary Stars (IDS), can be explained by a distribution of secondary masses according to the Initial Mass Function (IMF), i.e., ϕ(M)∞M−2.7.