In party-based autocracies, ruling parties’ relationship with their masses is critical for their survival. Previous literature has suggested that ruling party size drives durability. I propose a different approach: membership recruitment practices are repeated key challenges influencing the top-down and bottom-up balance, signaling elite cohesion and citizens’ interest in becoming party members. When ruling parties ensure membership stability, internal cohesion and returns to membership are constant, preventing abrupt volatility and increasing their durability. When these two factors are not aligned, ruling parties experience membership volatility (e.g., mass purges or recruitment), hindering their durability. Using an original dataset featuring 1,845 year-observations across 44 party-based autocracies between 1945 and 2020 and two novel measures of party membership, size and stability, I find that ruling parties with stable membership growth have longer durability than those experiencing volatility. Contrary to previous expectations, I also find that ruling party size does not influence their survival.