There were 146 B&W episodes that portrayed Dennis as the helpful menace that caused chaos. Dennis lived at 627 Elm Street next door to his best friend Mr. Wilson. Although Mr. Wilson did not consider himself to be Dennis' best friend. Dennis always was there to help Mr. Wilson whether he wanted the help or not. Joseph Kearns played Mr. Wilson until his death in 1962. He was the perfect Mr. Wilson. He was persnickety, a perfectionist, highly intelligent and best of all, he still liked Dennis in spite of his helpful misadventures.
Mr. Wilson gives Dennis a Gold watch in his will. Soon after that Mr. Wilson begins to feel old and is convinced that he has short time to live.
Dennis convinces Mr. Wilson to go to the Dentist for his tooth because Dennis thinks he can get a basketball from the Dentist until he learns that the Dentist only gives away prizes to child patients.
George Wilson's brother John Wilson comes to visit, only he has trouble working without his old cushion.
Dennis is all set for a big day. He is scheduled to have a fight with Gifford - the school bully.
Mr. Wilson gets mixed up with Gypsyes and they think he is one of them.
Dennis becomes confused about love when he hears his parents and Mr.& Mrs. Wilson argue with one another.
Dennis sees baby booties knitted for Mr. Wilson's golf clubs and he thinks that the Wilson's are having a baby, So he goes around and tells the whole neighborhood.
Dennis accidentally ties an important note that belongs to Mr. Wilson on a pigeon, so Mr. Wilson, Henry, Tommy and Dennis go to where the pigeons roost at night at a spooky house to try and get the note back and end up in the middle of a collage fraternity initiation meant for new fraternity members. After a bunch of twists and turns they find the pigeon with the note tied on it.
Mr. Wilson becomes a cat catcher for the police department to try and enforce a cat leash law.
Dennis and his friends decide to play Robin Hood and help Mr. Wilson(big John) when he is in trouble, only Dennis and his friends end up making things worse for Mr. Wilson.
Mr. Wilson disapproves of the way Dennis' school operates, So he writes his opinion to the newspaper and spends a day at school to observe.
Dennis and his friends start up a laundry business and clean Mr. Wilson's tuxedo, only Dennis gets Mr. Wilson's tuxedo mixed up with other peoples.
Mr. Wilson wants to represent Scotland for Dennis' School
Dennis is to write a composition for school about his best friend, and he chooses Mr. Wilson.
Henry gets a ticket for walking on the grass in the park. When Mr. Wilson hears about it he thinks it isn't fair, So he convinces Henry to go to court and contest it.
Mr. Wilson is supposed to take a picture of a plant that blooms briefly at night, but ends up dozing off when the time comes. Luckily, Dennis takes the picture of the flower for him.
Dennis overhears Mr. Wilson saying that he wishes he had his raccoon coat back. Dennis gives the story to the newspaper and, as a result, all day, people bring Mr. Wilson raccoon coats.
Dennis trains Mr. Wilson's dog Fremont, which backfires when Fremont will only listen to Dennis and ignores Mr. Wilson.
Dennis tries to take care of his sick mother while his father is out of town.
Mr. Wilson builds a barbecue in his backyard with help from Dennis' friend, Fred Baines. They then realize something valuable was left inside, and it must be torn down.
Dennis, his father, and Mr. Wilson camp out as pioneers to prove to Mr. Krinkie that they can live of the land like the pioneers.
Mr. Wilson accidentlly gets a space helmet that belongs to Dennis stuck on his head.
Dennis and Mr. Wilson camp out on a moutain so that Dennis can join the Junior Pathfinders club.
Mr. Wilson tricks Dennis into taking a silver coin that says GOOD LUCK and a horseshoe on it instead of 50 cents that he owes him for cutting his lawn. Mrs. Wilson is very angry with him about it. So, she and Alice start a scheme of their own by making lucky things happen to Dennis all day. Mr. Wilson soon starts to believe that the coin was lucky after all and is sorry he ever let it go. He then realizes that it was all a charade to teach him a lesson.
Henry tries to take Alice out on their Anniversary. Meanwhile Dennis tries to build a swing in his yard and ends up chasing a cat up a tree in the process.