An adjustable connector system for stay-in place formwork has a male adjustable connector end that can be inserted into a corresponding female adjustable connector end at variable positions. Using adjustable connector ends in assembling a formwork system increases accuracy by facilitating on-site adjustability of the length and/or diameter measurements of the system. The stay-in-place formwork can be used to create building surfaces, including ceiling panels, siding and walls, and can be used for forming concrete structures, such as walls and sumps.