Len Barry [[credited by his real name: Leonard Borisoff) wrote this with the Philadelphia songwriting/production team of John Madara and David White, who also wrote the hits "You Don't Own Me" and "At The Hop."

In an interview with Forgotten Hits, Madara explained: "In 1965, with '1-2-3' being the #1 record in the country, we were sued by Motown during the period when Berry Gordy was suing anyone whose records sounded like a Motown record. We were sued, saying that '1-2-3' was taken from a B-Side of a Supremes record called 'Ask Any Girl.' The only similarity between the two songs are the first three notes where the Supremes sang 'Ask Any Girl' and Lenny sang '1-2-3.' After that, there were no similarities, but their lawsuit said that our goal was to copy the Motown sound. Well, needless to say, Motown kept us in court, tying up all of our writers' royalties, production royalties and publishing royalties, and threatened to sue us on the follow-up to '1-2-3,' which was 'Like A Baby.' So after battling with them for two years and having a ton of legal bills, we made a settlement with Motown, giving them 15% of the writers' and publishers' share.
We never heard 'Ask Any Girl.' The only influence for making '1-2-3' was to make a ballad with a beat. And the sound of '1-2-3' was definitely the sound of the era. Listen to 'The In-Crowd' - that's not the Motown Sound, that's the sound of the era - and '1-2-3' definitely had a beat! Motown was suing a lot of people at the time."

http://www.songfacts.com/detail.php?id=4937