<p>Using MSSQL2005, can I truncate a table with a foreign key constraint if I first truncate the child table (the table with the primary key of the FK relationship)?</p>

<p>I know that I can either</p>

<ul>
<li>Use a <code>DELETE</code> without a where clause and then <code>RESEED</code> the identity (or)</li>
<li>Remove the FK, truncate the table, and recreate the FK.</li>
</ul>

<p>I thought that as long as I truncated the child table before the parent, I'd be okay without doing either of the options above, but I'm getting this error:</p>

<blockquote>
  <p>Cannot truncate table 'TableName' because it is being referenced by a FOREIGN KEY constraint.</p>
</blockquote>

Correct; you cannot truncate a table which has an FK constraint on it.
Typically my process for this is:
Drop the constraints
Trunc the table
Recreate the constraints.
(All in a transaction, of course.)
Of course, this only applies if the
child has already been truncated.
Otherwise I go a different route, dependent entirely on what my data looks like. (Too many variables to get into here.)
The original poster determined WHY this is the case; see
this answer
for more details.