There is renewed interest in the management of eastern white pine (Pinus strobus L.) for high-quality wood production. Several tree improvement programs have been implemented for the last few decades to better understand the genetic variability of eastern white pine. However, the genetic variation of eastern white pine has been evaluated mostly by comparing diameter or height growth of different families or provenances in common gardens with pure plantations. Growth comparison is insufficient because it does not evaluate the efficiency of different families to use site resources for productivity improvement. Crown attributes have received less consideration in genetic studies on eastern white pine. The objective of this study was to compare the performance of 25 eastern white pine families growing in mixed plantations with grey alder (Alnus incana [L.] Moench). Branch development traits and relative measures of crown development were used to compare the families. The results indicated that the variance components of the family effect were not significant for the dbh (diameter at breast height) and height growth variables and the different measures of crown development. The lack of significant variation among the 25 families was also observed for branch increment rate, the relationship between branch length and branch diameter and the relationships between diameter growth rate in terms of absolute and relative growth rates and a competition index. Thus, different families responded similarly to the effect of competition from grey alder. For all these relationships, the results also indicated that the variation in microsite conditions accentuated the differences in the family variance components.