Let Me Hear Your Voice is an early book reporting one families' success using behavior therapy as an early intervention for autism. It echoes the continuing truth that the earlier you catch and treat autism, the better your likely outcome. I would have loved an updated edition that discussed how her children faired as they grew.
As other reviews stated, the specific techniques referenced in this book are a bit outdated, though Lovaas' place as a pioneer in behavioral analysis deserves reiterating.
I would not recommend this as a first book to read on the subject, but it is still nice to hear of the successes.