The district currently includes central and eastern portions of San Diego, as well as eastern suburbs such as El Cajon, La Mesa, Spring Valley, and Lemon Grove.

The 51st and 50th are partitioned by Camino del Norte, Highway 15, Carmel Mountain Rd, Ted Williams Parkway, Del Mar Mesa Openspace, Los Penasquitos Creek, Inland Freeway, Governor Dr, Pavlov Ave, Stetson Ave, Millikin Ave, Regents Rd, Ducommun Ave, Bunch Ave, Branting St, Streseman St, Pennant Way, Highway 52, San Diego Freeway, Sea World Dr, Friars Rd, Kumeyaay Highway, and Highway 805.

The 51st district takes in the cities of El Cajon, Lemon Grove, and La Mesa, as well as the census-designated places La Presa and Spring Valley.

It also encompasses the San Diego neighborhoods of Paradise Hills, Mira Mesa, Miramar, San Carlos, Sorrento, Clairemont, Normal Heights, Allied Gardens, Grantville, Balboa Park, Linda Vista, and Serra Mesa.

Randy "Duke" Cunningham won the Republican nomination and won the general election by just a point, meaning that the San Diego area was represented entirely by Republicans for only the second time since the city was split into three districts after the 1960 United States census.