“It’s surprising partly because of the size of the decline in a short period,” said Cary Funk, a senior researcher at Pew. “We’re seeing an increase in religious pluralism among Hispanics, and also greater polarization on the religious spectrum.”

The Pew survey was conducted in English and Spanish with 5,103 Hispanic adults in the United States; the telephone poll was done by landline and cellphone in the spring and summer of last year, and has a margin of sampling error of plus or minus 2 percentage points.

Previous research has noted that Hispanics in the United States are leaving religion as they assimilate to a more broadly secular culture. The Pew poll finds the rise in the number of Hispanics who say they are unaffiliated particularly pronounced among Hispanics under age 30, and it comes at a time when more and more Americans are becoming part of what religion researchers call “the nones,” people who say they are not affiliated with a religious tradition.

Asked why they left their childhood faith, the two most often-cited responses were that they just “drifted away,” or that they stopped believing in church teachings.

​The Catholic Church has been working for years to increase its ministry to Hispanics. In a blog post this week, Sister Mary Ann Walsh, the spokeswoman for the U.S. Conference of Catholic Bishops, noted that the church is now requiring many seminarians to learn Spanish, that there has been an increase in the number of Hispanic deacons, and that ​​there are Hispanic bishops heading several large dioceses, including in Los Angeles, San Antonio, Sacramento and San Diego.​

But she acknowledged the challenge.

“​Everyone, including Hispanics, and especially young ones, can fall prey to what has become a new American problem, religious relativism, where, perhaps inspired by exciting music or a rousing preacher, you move from your parents’ church to another to no church at all,” she wrote. She added, “It is scary to consider that religious relativism may be the greatest threat that exists to the increasingly important Hispanic Catholic community.”