A collection of fleas was acquired independently from Costa Rica by two different field teams. Among these collections were a sizable series of Kohlsia mojica Tipton and Méndez which were previously reported only from the northern province of Bocas del Toro, Panama. These new records were present in two provinces of Costa Rica (Alajuela and Puntarenas). Additional specimens discovered in the Robert Traub flea collection in the Carnegie Museum of Natural History, heretofore unreported, included specimens from San Jose and Cartago provinces, Costa Rica. The primary host for K. mojica is the Mexican deer mouse, Peromyscus mexicanus Saussure. Collectively, five species of Kohlsia have been reported within the geographical boundaries of Costa Rica and Panama [K. mojica, K. azuerensis Tipton and Méndez, K. keenani Tipton and Méndez, K. graphis graphis (Rothschild), and K. traubi Tipton and Méndez]. A key is provided for these five species. Specimens of K. g. graphis are reported herein for the first time from Guatemala and Mexico, and the variegated squirrel Sciurus variegatoides Ogilby represents a new host record for K. g. graphis. Table 1 is included to illustrate the distribution of all known Kohlsia species. In addition, Kohlsia campaniger Jordan (an extralimital species) described from a single female specimen from Ecuador is discussed. Several morphological characters are provided to distinguish K. campaniger and Kohlsia felteni Smit. Jellisonia ortizi Vargas (currently valid in Kohlsia) is hypothesized to be a new synonym of Kohlsia fournieri Vargas. Kohlsia keenani is reported for the first time from Handleyomys alfaroi (J. A. Allen), Handleyomys chapmani (Thomas) and Nephelomys albigularis (Tomes).