From the ever entertaining (and, of course, useful), PUBMED search:
Radun I, Summala H.Females do not have more injury road accidents on Friday the 13th.
BMC Public Health. 2004 Nov 16;4:54.
Exadaktylos AK, Sclabas G, Siegenthaler A, Eggli S, Kohler HP, Luterbacher J. Friday the 13th and full-moon: the "worst case scenario" or only superstition? Am J Emerg Med. 2001 Jul;19(4):319-20.
Veale D. Friday the 13th and obsessive compulsive disorder. BMJ. 1995 Oct 14;311(7011):963-4.
Scanlon TJ, Luben RN, Scanlon FL, Singleton N.Is Friday the 13th bad for your health? BMJ. 1993 Dec 18-25;307(6919):1584-6
I especially like the conclusion sentence of the last abstract. That is, "Staying at home is recommended."