opposite, polar
Their views are at opposite extremes from each other.

logical
new
She has taken cleanliness to a new extreme.

climatic, political, temperature
It's a difficult place to live because of its climatic extremes.

avoid
Avoid any extremes of temperature.

go to, reach
There is no need to go to such extremes.

carry sth to, take sth to
It's foolish to take any dieting to extremes.

represent

at an/the extreme
At the extreme, some nuclear waste is so radioactive it has to be kept isolated for thousands of years.

between extremes
There has to be a solution between these extremes.

in the extreme
His voice was scornful in the extreme.

to the extreme
She was always generous to the extreme.

extremes of
These photographs show extremes of obesity and emaciation.

at one extreme, at the other extreme
At the other extreme, women still childless at 32 were more likely to be from a professional background.

go from one extreme to the other
She goes from one extreme to the other, and either works very hard or does absolutely nothing.

go to the opposite extreme, go to the other extreme
After always putting too much salt in her cooking, she went to the opposite extreme and banished it completely.

be
appear, seem, sound
become
consider sth

particularly, really, very
a bit, fairly, a little, quite, rather, somewhat
Some of his views seem rather extreme.

at its most extreme
This is hero-worship at its most extreme.

Extreme is used with these nouns:
agitation, agony, altitude, brutality, care, case, caution, circumstance, climate, close-up, cold, complexity, condition, corner, cruelty, danger, degree, delicacy, deprivation, difficulty, disappointment, discomfort, dislike, displeasure, distaste, distress, drought, emergency, emotion, end, environment, envy, example, excitement, exertion, exhaustion, fatigue, form, gravity, hardship, heat, hostility, hunger, imbalance, importance, instance, jealousy, left, limit, manifestation, measure, nationalism, nationalist, nervousness, old age, pain, paranoia, politics, position, poverty, precision, provocation, reaction, reluctance, repression, right, scepticism, sensitivity, shyness, simplicity, sport, stress, subtlety, tactic, temperature, tiredness, top, type, urgency, variability, variation, version, view, violence, vulnerability, weather, wing, youth