In this proceeding we present the method and results of the search for galaxy groups or clusters in the vicinity of the line-of-sight towards lensed quasars.We have studied a sample of ten quasars, using deep ESO/VLT FORS1 and ISAAC images, as well as archive HST/WFPC2 and NiCMOS data. We find that there is most probably a galaxy group towards CTQ 414, HE 0230-2130, B 1359+154, H 1413+117, SBS 1520+530 and HE 2149-2745, with masses $\leq$4~10$^{14}$M$_\odot$h$^{-1}$. Considering its photometric redshift, the galaxy group discovered in the field around HE 1104-1805 is associated with the quasar rather than with the lensing potential. We also conclude that the pair LBQS 1429-0053-A and LBQS 1429-0053-B is a genuine binary quasar rather than a lensed quasar.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html