We present a VI photometric catalogue towards the open cluster Cr 121 .
XMM-Newton and ROSAT data are used to discover a low-mass pre-main sequence ( PMS ) along this sight-line . ( ) identified Cr 121 as a moving group , using HIPPARCOS data , at a distance of 592 pc .
We reject the scenario that these low-mass PMS stars are associated with that association .
By considering the higher mass main sequence stellar membership of the groups along this sight-line , the density of low-mass PMS stars and their age spread we argue that the low-mass PMS stars are associated with a young , compact cluster at a distance of 1050 pc .
This is consistent with the original description of Cr 121 ( ) , and we argue that this distant compact cluster should retain its original designation .
The moving group detected by ( ) 
resembles a foreground association and we agree with ( ) that this should be called CMa OB2 .

This study demonstrates that although the ( ) census of OB associations is an invaluable resource for studying local star formation , it must be interpreted in the context other data when considering structure over distances of the same order as the limits of the Hipparcos parallaxes .