Sylvia Sidney was born in New York City, in the Bronx borough, on August 8, 1910 with the birth name of Sophia Kosow. Her father was Russian born and her mother was born in Romania. They divorced not long after her birth. Her mother subsequently remarried and Sylvia was adopted by her stepfather, Sigmund Sidney. Sylvia was a shy child and her parents tried to encourage her to be more outgoing and gregarious. As an early teen, Sylvia had decided that she wanted a stage career. While most parents would have looked down on such an announcement, Sylvia was encouraged to pursue the dream she had made. She was enrolled in the Theater Guild's School for Acting. Sylvia later admitted that when she decided to become a stage actress at 15, it wasn't being starstruck that occurred to her, but the expression of beauty that encompassed acting. All she wanted was to be identified with good productions. One school production was held at a Broadway theater and in the audience there was a critic from the New York Times who had nothing but rave reviews for the young Miss Sidney. On the strength of her performance in New York, Sylvia appeared in a play at the famed Poli Theater in Washington, D.C. More stage productions followed, each better than the last and it wasn't long before the film moguls were at the doorstep. Sylvia was appearing in the stage production of "Crime" when she made her first appearance on the silver screen in 1927. The film in question was "Broadway Nights" which was dealt with stage personalities of which Sylvia was one. After the film she returned to the stage where she appeared in creations which were, for the most part, forgettable.