Portnoy’s Complaint returns frequently to the theme of Jewish identity. As Alex explores his memories, his Jewish identity and his relationship with the Jewish community are a cornerstone of his psychological understanding of the world. Alex’s Jewish identity is consistently reinforced by others, whether in negative contexts like the antisemitism that forces the family to move to New Jersey or positive ones like the Jewish he lives in as a teen. Through his family keeping kosher, his father taking him to the bathhouse, or community softball games, Jewish identity is the ambient backdrop to Alex’s life. Simultaneously, Alex expends a lot of effort trying to escape his Jewish identity. Whether through dating gentile girls, spending Thanksgiving in the Midwest, or trying to lose himself in the hustle and bustle of New York City, Alex tries and fails to divorce himself from the ethnic and cultural context in which he was born and raised. Even as Alex tries to reject Judaism, though, it shapes his narration and search for identity.

Alex feels like an outsider in American society. He observes the gentiles around him and envies that society is built around them as the majority. The ubiquity of Christmas as a seasonal festival, for example, remains alien to him as something he is exposed to but still unable to participate in.