There have been 60 NBA Finals. The Boston Celtics have won 17, and the Minneapolis/Los Angeles Lakers have won 15, which amounts to those teams winning more than half of all NBA Finals. This year, they play each other in the Finals again, making it 33 champions out of 61 being either the Lakers or the Celtics.
Additionally, 39 of the 61 Finals have included either the Lakers or the Celtics. Including this year, the Celtics and Lakers have played each other in the Finals a whopping 12 times (just under one-fifth of all Finals have been these two teams).
The Celtics have made 21 total Finals appearances, so have faced the Lakers more than half of the times they've been in the Finals. The Lakers have made 30 Finals appearances, facing the Celtics in two-fifths of those.
The Celtics won nine of those against the Lakers, which accounts for more than half of all their 17 championships. The Lakers' two victories over the Celtics came after the Celtics won their first eight encounters.
The longest streak without either team in the Finals was eight years from '92-'99. The longest streak with either the Lakers or Celtics in the Finals was 10 years, done twice (from '57-'66, in which the Celtics appears all 10 years, and the Lakers five of those; and '80-'89, in which the Lakers appeared eight times, the Celtics five).
The longest streak for one team appearing in the Finals was, as noted, Boston, in the 10 years from '57-'66. Boston won nine of those 10 years, including eight in a row (the longest winning streak from any one team) from '59-'66, and also won 10 in 12 years, from '57-'69.
The Lakers' longest appearance streak is "only" four, from '82-'85, winning twice; but they have also appeared three times in a row five additional times (including the current three-year streak). In two of those, they won all three years; in one, they lost all three.
The only other team to "threepeat" was the Bulls, winning three years in a row twice in eight years ('91-'98). No other team but the Celtics and Lakers have had four consecutive appearances. The only other team to have three consecutive appearances was the Knicks, losing all three from '51-'53.
The 2010 NBA Finals begin in Los Angeles on Thursday.