The four-story, 75,000-square-foot center, scheduled to open in the spring of 2011, will provide a variety of diagnostic, treatment and support services in one location.
Beginning at noon, guests will have an opportunity to sign the beam, after which a 160-foot crane will swing it into place at about 1:15 p.m.
Hundreds of community leaders and construction workers plan to gather to celebrate the progress.
Today's program will begin at noon at the corner of Los Gatos Boulevard and Samaritan Drive, near state Highway 85. The beam placement can be viewed from the top of an adjacent parking structure.