No, you do not have to do a prelim year. Most schools only require that you dedicate only 6 months of your intern year to primary care. Typically it includes 2-4 months of inpatient Medicine/Peds/ER and 1-2 months of OUTPATIENT Medicine/OB as well as a month of Inpatient or Consult Neurology. Pretty cool, huh? It varies by program as to how much you do of each speciatly but 90% of the programs I looked at when applying for residency only required 6 months of non-psych work.