This paper reviews the results of early cellphone studies, where exposure 
duration was too short to expect tumorigenesis, as well as two sets of more 
recent studies with longer exposure duration: the Interphone studies and the 
Swedish studies led by Dr. Lennart Hardell. The recent studies reach very 
different conclusions. With four exceptions the industry-funded Interphone 
studies found no increased risk of brain tumors from cellphone use, while the 
Swedish studies, independent of industry funding, reported numerous findings of 
significant increased brain tumor risk from cellphone and cordless phone use. An 
analysis of the data from the Interphone studies suggests that either the use of 
a cellphone protects the user from a brain tumor, or the studies had serious 
design flaws. Eleven flaws are identified: (1) selection bias, (2) insufficient 
latency time, (3) definition of 'regular' cellphone user, (4) exclusion of young 
adults and children, (5) brain tumor risk from cellphones radiating higher power 
levels in rural areas were not investigated, (6) exposure to other transmitting 
sources are excluded, (7) exclusion of brain tumor types, (8) tumors outside the 
cellphone radiation plume are treated as exposed, (9) exclusion of brain tumor 
cases because of death or illness, (10) recall accuracy of cellphone use, and 
(11) funding bias. The Interphone studies have all 11 flaws, and the Swedish 
studies have 3 flaws (8, 9 and 10). The data from the Swedish studies are 
consistent with what would be expected if cellphone use were a risk for brain 
tumors, while the Interphone studies data are incredulous. If a risk does exist, 
the public health cost will be large. These are the circumstances where 
application of the Precautionary Principle is indicated, especially if low-cost 
options could reduce the absorbed cellphone radiation by several orders of 
magnitude.