Summary: This paper studies a dynamic insurance problem with bilateral asymmetric information and balanced budgets. There are two infinitely-lived agents in our model, both risk averse, and each as an i.i.d. random endowment stream which is unobservable to the other. In each period, each agent must have a non-negative consumption and together they must consume the entire aggregate endowment. Dynamic incentive compatibility in the Nash sense is defined. We give sufficient and necessary conditions for the existence of a constrained efficient contract. We show that a constrained efficient contract can be characterized in a Bellman equation. We demonstrate that the long-run distribution of expected utilities of each agent is not degenerate. We also develop an algorithm for computing the efficient contract and, in a numerical example, we find that the consumption processes of the agents form stationary Markov chains.