Misjoinder of causes of action occurs when the conditions for joinder under Rule 2, Section 5 are not met. It is not a ground for the dismissal of an action.

The conditions for joinder include complying with the rules on joinder of parties, not including special civil actions or actions governed by special rules, and meeting specific requirements regarding venue or jurisdiction when causes of action pertain to different ones but are between the same parties. For instance, an ordinary civil action cannot be joined with a special civil action like partition or foreclosure of mortgage. When there are multiple parties, joinder of causes of action requires that the right to relief arises out of the same transaction or series of transactions and that there is a question of law or fact common to all the parties.

The remedy for a misjoined cause of action is severance. The misjoined cause of action may be severed and proceeded with separately upon motion of a party or on the court's own initiative.

If there is no objection to the improper joinder or the court does not motu proprio direct severance, simultaneous adjudication of the erroneously joined causes of action is permissible. This is allowed as long as the court trying the case has jurisdiction over all the causes of action therein, notwithstanding the misjoinder. However, if the court lacks jurisdiction over a misjoined cause of action, it must be severed; otherwise, any adjudication concerning it would be a nullity. Misjoinder of causes of action is distinct from splitting a single cause of action, which is prohibited and can lead to dismissal.