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We present further arguments that the Hipparcos parallaxes for some of theclusters and associations represented in the Hipparcos catalog should be usedwith caution in the study of the Galactic structure. It has been already shownthat the discrepancy between the Hipparcos and ground based parallaxes forseveral clusters including the Pleiades, Coma Ber and NGC 6231 can be resolvedby recomputing the Hipparcos astrometric solutions with an improved algorithmdiminishing correlated errors in the attitude parameters. Here we present newparallaxes obtained with this algorithm for another group of stars withdiscrepant data - the galactic cluster Cr 121. The original Hipparcosparallaxes led de Zeeuw et al. to conclude that Cr 121 and the surroundingassociation of OB stars form a relatively compact and coherent moving group ata distance of 550 -- 600 pc. Our corrected parallaxes reveal a differentspatial distribution of young stellar populace in this area. Both the clusterCr 121 and the extended OB association are considerably more distant (750 --1000 pc), and the latter has a large depth probably extending beyond 1 kpc.Therefore, not only are the recalculated parallaxes in complete agreement withthe photometric uvbybeta parallaxes, but the structure of the field they revealis no longer in discrepancy with that found by the photometric method.

The Structure and the Distance of Collinder 121 from Hipparcos and Photometry: Resolving the Discrepancy