It's also possible you need the other index instead, rather than in addition to, the one you have know.
You always need to look at the usage stats too when looking at the missing index stats.
And, as noted, take SQL's recommendations with extreme caution. SQL always wants an index, even if it's not really justified when you consider all information about the table.
SQL DBA,SQL Server MVP('07, '08, '09)
Prosecutor James Blackburn, in closing argument in the "Fatal Vision" murders trial: "If in the future, you should cry a tear, cry one for them [the murder victims]. If in the future, you should say a prayer, say one for them. And if in the future, you should light a candle, light one for them."