Achieving 100% completion in Grand Theft Auto IV requires dedication and thoroughness, as it involves completing all main missions, side activities, and collecting every hidden item. This guide will outline all the requirements to reach this prestigious milestone.

Requirements for 100% Completion:
- Complete All Main Story Missions: Finish the entire narrative, including the final choice and its consequences.
- Complete All Assassination Missions: Available from a payphone after meeting Phil Bell. There are 9 missions.
- Complete All Car Thefts for Stevie: After meeting Brucie, you'll unlock car theft missions for Stevie. There are 30 cars to find and deliver.
- Complete All Exotic Exports for Brucie: Deliver 10 specific cars to Brucie's garage.
- Complete All Vigilante Missions: Eliminate all 30 'Most Wanted' targets (10 per major island group).
- Complete All 10 Drug Delivery Missions for Little Jacob: After unlocking his perk, call him for jobs.
- Complete All 9 Races for Brucie: Win all street races.
- Complete All 50 Unique Stunt Jumps: Successfully land all unique jumps.
- Shoot All 200 Pigeons: Find and eliminate every flying rat.
- Win at All Mini-Games: Win at least once at Pool, Darts, and Bowling.
- Complete All Friend Activities: Hang out with Roman, Little Jacob, Packie, and Dwayne at least once for each activity they enjoy (Bowling, Darts, Pool, Eating, Drinking, Strip Club, Show).
- Complete All Girlfriend Dates: Go on at least one date with Michelle, Carmen, Kiki, and Alexandra.
- Unlock All Special Abilities: Achieve 75% 'Like' with Roman, Little Jacob, Packie, and Dwayne.
Tips for 100% Completion:
- Use a Checklist: Keep track of your progress, especially for collectibles like pigeons and stunt jumps.
- Prioritize Side Content: Many side activities become available early. Tackle them gradually to avoid burnout.
- Save Frequently: Especially before attempting challenging jumps or missions.
- Utilize Guides: For pigeon locations and stunt jumps, external maps or video guides are invaluable.
- Enjoy the Journey: Don't rush. 100% completion is a marathon, not a sprint.
Upon reaching 100%, you'll receive an achievement/trophy and a special message in-game, confirming your mastery of Liberty City.